Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV2: Novel Techniques and Sources II
Monday PM, November 26, 2012
Sheraton, 2nd Floor, Independence W
2:30 AM - *VV2.01
X-Ray Free Electron Lasers: New X-Rays for New Science
Jerome Hastings 1
1SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
X-ray free electron lasers (FEL) are now operational worldwide spanning wavelengths from 0.07-30 nm. This presentation will describe briefly self-amplified spontaneous emission (SASE), the principle underlying FELs and extensions to approach a fully coherent x-ray source at nm wavelengths. This discussion naturally leads to a description of the properties of the x-ray beams. Finally some details of existing and planned FELs worldwide will be discussed.
3:00 AM - VV2.02
Time Resolved Small Angle X-Ray Scattering Measurements in Foams and Metals Loaded in High Rate Compression
Tony van Buuren 1 Jim McNaney 1 Bassem El-Dasher 1 Jim Hawreliak 1 Despina Milathianaki 3 Jan Ilavsky 2 Tim Graber 2 Robert Henning 2
1LLNL Livermore USA2Argonne National Laboratory Chicago USA3SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Nanofoams are considered an essential component for high energy density physics experiments because they provide a convenient method to independently vary density without changing atomic number. Since the dynamics of its collapse upon implosion plays an essential role in achieving inertial confinement fusion, characterizing the performance of low density materials under these extreme conditions provides crucial feedback in developing materials with optimal properties. In order to achieve this understanding, it is crucial to directly probe the controlling phenomena, in-situ and in real time. Recently, we have successfully developed the capability of measuring small angle x-ray scattering using a single x-ray pulse, thus enabling the use of pump-probe experiments to measure structural changes in-situ during a shock. Compression of under-dense materials under dynamic loading condition has been studied for some time using a variety of techniques. The significant momentum involved in these dynamic compaction events make it nearly impossible to study the evolution of such systems ex-situ. As a result, experimental information concerning the rate of collapse and morphological changes associated with void closure are lacking. Likewise, the early stages of void formation in dynamically driven spall are also difficult to observe experimentally. We have developed a system to investigate both void formation, during spall in metals, and void collapse, in under-dense carbon aerogel foams, using time resolved small angle x-ray scattering at the Advanced Photon Source. The system utilizes a laser to generate ablatively driven loading and use of a standard X-ray scattering camera along with a chopper based single bunch isolator. The carbon based foam materials begin with significant levels of scattering and dramatic changes are observed during loading and release of the compression wave. During compression a decrease in the total scattering intensity and the average pore diameter are observed consistent with a collapse of the pore structure in the nanoporous carbon. Evolution of the foam structure continues with during release of the compression wave where large structures are observed in the scattering potential due to the breakup of the nanoporous carbon. Effects of initial carbon microstructure and the compression wave condition on the time scale for the pore collapse are explored.
3:15 AM - VV2.03
Viewing Nanocrystal Structural Changes with Femtosecond Resolution
Timothy Alan Miller 1 Joshua S. Wittenberg 1 Aaron M. Lindenberg 1 2 3
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USA3SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Nanocrystals provide ideal systems with which to study structural phase changes. By making use of the ultra-short pulsed nature of synchrotrons and free-electron lasers, one may visualize with atomic-resolution and in real time how nanosized systems rearrange and potentially resolve the transition state itself. Such information could lead to new material design opportunities in which the phase-change behavior is optimal for a given application. Here we present ultrafast studies of both temperature and pressure-driven phase changes in nanocrystalline materials, utilizing x-ray diffraction and x-ray spectroscopy to monitor the atomic rearrangement on femtosecond time-scales. For a thermally-driven phase change, we consider the onset of superionicity, a unique superposition of liquid-like cationic conductivity within a solid-phase anionic lattice. Using near-edge spectroscopy, we observe the superionic structural transformation to occur faster than twenty picoseconds in laser-excited copper (I) sulfide nanocrystals, and show that it is the ionic hopping time which determines this time-scale. For pressure-induced studies, we investigate the dynamics of the well-known change of cadmium selenide nanocrystals from a wurtzite to rock-salt unit cell under increasing pressure. We use laser-induced shock compression to initiate the phase transformation and hard x-ray scattering techniques as a probe. . By using oriented films, we consider the effect of crystallographic direction on the structural pathway during the phase change, as well as the effect of nanocrystal shape.
3:30 AM - *VV2.04
Structural Dynamics of Polycrystals under Shock Compression Observed via Nanosecond Time-resolved X-Ray Diffraction
Kazutaka G Nakamura 1 Jianbo Hu 1 Kouhei Ichiyanagi 2 Shin-ichi Adachi 3
1Tokyo Institute of Technology Yokohama Japan2University of Tokyo Tokyo Japan3High Energy Accelerator Research Organization Tsukuba JapanShow Abstract
Investigation on phase transitions of materials under shock compression has bottlenecked due to the limitation of traditional experimental approaches that provide incomplete information on structural dynamics. Time-resolved x-ray diffraction enables to monitor time evolution of crystal structure under shock compression. We demonstrated direct observation of shock-induced phase transition of polycrystalline zirconia ceramics (3 mol % Y2O3 stabilized tetragonal zirconia: 3Y-TZP) and bismuth via nanosecond time-resolved x-ray diffraction with a single-shot laser pump and x-ray probe scheme. The experiment was performed using the beamline NW-14A at the Photon Factory Advanced Ring, KEK Japan. The x-ray pulse from an undulator with the period length of 20 mm (U20) has the pulse duration of approximately 100 ps, the energy of 15.6 KeV, the bandwidth of 4.4 % and the flux of 3x108 photons/pulse. The nanosecond laser pulse (1064 nm, 700 mJ) was focused on the target assembly with a plasma-confinement geometry in order to induce shock compression. The Debye-Scherrer diffraction pattern was recorded on an x-ray CCD. For 3Y-TZP, the martensitic phase transformation from the tetragonal structure to the monoclinic structure, which is the stable phase for pure zirconia at ambient pressure and temperature, has been observed during shock compression at 5 GPa within 20 ns without any intermediates. This monoclinic structure reverts back to the tetragonal structure during pressure release. The results imply that the stabilization effect due to the addition of Y2O3 is to some extent negated by the shear stress under compression. For polycrystalline bismuth, the nanosecond time-resolved x-ray diffraction showed new diffraction peaks during both shock compression and release at the shock pressure of 5 GPa. The results reveal that structural phase transitions from Bi-I to Bi-III during compression and from Bi-III to Bi-I via Bi-II during release occur.
VV3: Functional Materials and Local Order I
Monday PM, November 26, 2012
Sheraton, 2nd Floor, Independence W
4:30 AM - *VV3.01
Polymer Micelles and Functionalized Interfaces
Andreas Magerl 1
1University of Erlangen-Namp;#252;rnberg Erlangen GermanyShow Abstract
Functionalized surfaces/interfaces are highly relevant both in present basic research and for numerous applications. Examples are the heat transfer through glass windows which can be lowered or the flow of liquids in pipelines which can be increased by appropriate coatings leading in the end to more energy-efficient systems. We have engaged in a broad study of the structures of triblock-copolymer solutions with particular emphasis on Pluronic P123 [PEO20PPO70PEO20] which shows a rich phase behavior depending on temperature and concentration. SAXS and SANS measurements show a transition from unimers in solution to the formation of spherical micelles followed at higher temperature by a morphological change to elongated micelles. We argue that this phase transition is driven by a limited stability of the aggregates if a size parameter exceeds a critical value of 190 Å. Grazing incidence neutron diffraction in higher concentrated solutions reveal a crystallization with a structural transition from cubic to hexagonal which seems to be related again to the morphological stability of the individual micelles. Surprisingly, we find a pronounced thermal hysteresis for this phase transition. The polymer is found to coat hydrophilic surfaces while no attachment is observed for hydrophobic surface terminations. The process of hydrophobic coating with self-assembled monolayers from trichlorosilanes followed by in-situ synchrotron reflectivity measurements will be presented. While the packing is dense for amorphous oxide surfaces, the data reveal reduced packing densities for single crystalline materials where the degree of dilution depends on the structure of the oxide. In addition, distinctly different growth modes are found for crystalline and amorphous SiO2, while the macroscopic contact angles for water are about 110° in both cases. For hydrophilic surface terminations we find a complex sequence for the adsorption of unimers and micelles depending on temperature and concentration. These dense surface coatings build up already under conditions where there are no micelles in the bulk liquid. Again, the surface coatings show a thermal hysteresis which show great resemblance to bulk the properties observed at much higher concentration and temperature. Further, the mechanical stability of the surface coating and its recovery after destruction by shear will be reported on.
5:00 AM - VV3.02
Combined Computational and In-situ Neutron Scattering and Conductivity Studies of Superionic Lithium Borohydride
Bill David 1 2
1Rutherford Appleton Laboratory Chilton United Kingdom2University of Oxford Oxford United KingdomShow Abstract
Lithium borohydride is a remarkable material. It is not only a candidate in its own right as a high wt% hydrogen store but also exhibits superionic conductivity above 1080C which may be significant for lithium battery electrolytes. Moreover, lithium borohydride readily accommodates almost four times its own weight of ammonia and can intercalate other molecules such as methylamine. Combined with lithium amide, it forms mixed lithium borohydride amide compounds with low melting points and promising hydrogen desorption profiles. A similar eutectic behaviour is found when lithium borohydride is reacted with calcium and magnesium borohydride. All these properties are believed to result from the highly dynamic atomic behaviour of both Li+ and BH4- ions. This presentation will discuss recent in-situ studies of lithium borohydride involving combined ionic conductivity and neutron powder diffraction experiments that are discussed within the context of computational modelling using DFT non-equilibrium molecular dynamics. The in-situ conductivity measurements confirm that there is no intermediate phase in the vicinity of the orthorhombic-tetragonal phase transition and that the continuous change in conductivity may be explained by the co-existence of both high and low temperature phases. Computational modelling of the phase transition using non-equilibrium DFT molecular dynamics (NEMD) shows that the first-order phase transition is principally order-disorder in character although there is a significant displacive computation. Diffusion coefficients and conductivity values obtained from the NEMD-DFT calculations are in good agreement with the in-situ conductivity measurements.
5:15 AM - VV3.03
Simultaneous Neutron Diffraction and Thermogravimetric Studies of Hydrogen Storage Materials
Martin Owen Jones 1 Bill David 1 2 Joshua Makepeace 2
1ISIS, STFC Didcot United Kingdom2University of Oxford Oxford United KingdomShow Abstract
Hydrogen has been identified as a fuel of choice for providing clean energy for transport and other applications, and the development of materials to store hydrogen efficiently is key to this endeavour. Lightweight hydride materials have been promoted as potential hydrogen storage materials due to their high gravimetric and volumetric hydrogen storage capacities. Neutron scattering is the ideal tool to study hydrogen storage materials as hydrogen has the largest scattering interaction with neutrons of all the elements in the periodic table. To investigate the synthesis, structure, composition and decomposition of lightweight hydride systems we have developed novel apparatus that allows us to perform time-resolved simultaneous neutron diffraction and thermogravimetric measurements on materials using the GEM and HRPD diffractometers at ISIS. This apparatus, termed the Intelligent Gravimetric Analysis for Neutrons (IGAn, Figure 1), permits us to dynamically investigate hydrogenation and dehydrogenation processes within hydrogen storage materials. This apparatus, in conjunction with other techniques that include time-resolved X-ray synchrotron diffraction, thermogravimetric analysis with simultaneous mass spectroscopy and inelastic neutron scattering, allows us to develop a complete understanding of lightweight hydrogen storage materials. Here, we report the results of our simultaneous neutron diffraction and thermogravimetric studies into a prototypical lightweight hydride family, group 1 alkali metal amides (MND2, where M = Li, Na, K), using the IGAn apparatus. Our studies focus on the formation of MND2 from the reaction of MH with ammonia and subsequent temperature resolved decomposition. The role of time-resolved, simultaneous, neutron scattering techniques in understanding the complex chemistry that occurs on formation, decomposition and cycling of this family of materials is discussed.
5:30 AM - VV3.04
Diffraction from Vibrating Crystals: From Ultrasound to Phonons
Klaus-Dieter Liss 1 Andreas Magerl 2
1Australian Nuclear Science and Technology Organisation Lucas Heights Australia2Friedrich-Alexander-Universitamp;#228;t Erlangen-Namp;#252;rnberg Erlangen GermanyShow Abstract
The excitation of ultrasonic waves in perfect crystals can lead to interesting phenomena in neutron and X-ray diffraction, such as peak broadening caused by the lattice strain gradient, satellite reflections due to the space and time modulated structure, inelastic scattering, and caustics of the beam paths. Furthermore, spatially resolved diffraction on ultrashort time scales leads to the characterization of standing waves and shock waves. White beam Laue section topography is very sensitive to spatial wave field arrangements and shows up the transition between the dynamical and the kinematic theory of diffraction. The presentation reviews the concepts on our older work, gives unpublished experimental results and an outlook to the state-of-the-art and future capabilities of technological development, and their applications in materials science and physics.
VV1: Novel Techniques and Sources I
Monday AM, November 26, 2012
Sheraton, 2nd Floor, Independence W
9:30 AM - *VV1.01
Diffraction before Destruction: Imaging with an X-Ray Free-electron Laser
Henry N. Chapman 1 2 Anton Barty 1
1DESY Hamburg Germany2University of Hamburg Hamburg GermanyShow Abstract
The ultrafast pulses from X-ray free-electron lasers have opened up a new form of nanocrystallography for structure determination of molecules. These pulses are of high enough intensity and of sufficiently short duration that individual single-shot diffraction patterns can be obtained from a sample before significant radiation damage occurs. This “diffraction before destruction” method may enable the determination of structures of proteins that cannot be grown into large enough crystals or are too radiation sensitive for high-resolution crystallography. Ultrafast pump-probe studies of photoinduced dynamics in proteins or other materials can also be studied. We have carried out experiments in coherent diffraction from protein nanocrystals, including membrane bound proteins, at the Linac Coherent Light Source (LCLS) at SLAC. The crystals are delivered to the pulsed X-ray beam in a continuously flowing liquid jet. Millions of diffraction patterns were recorded at the LCLS repetition rate of 120 Hz. These patterns are indexed and combined into a single crystal diffraction pattern, which can be phased for structure determination. Details of the methodology, new opportunities for phasing, and novel applications will be discussed
10:00 AM - VV1.02
Direct Measurement of Microstructural Avalanches Using Coherent X-Ray Scattering
Michael C. Rogers 1 Mark Sutton 1 Karl F. Ludwig 2
1McGill University Montreal Canada2Boston University Boston USAShow Abstract
The functionality of shape memory alloys depends on the martensitic phase transition of the material, which involves the transformation from one crystalline phase to another. Despite the wide use of such materials, the rearrangement of atoms that facilitates their structural transformations is not well understood. We have developed an experimental technique that enables in-situ, real-time measurements of these structural transformations. This technique utilizes the high degree of coherence available from synchrotron x-rays to produce modulations, or ``speckle'', in the materials scattering pattern. Fluctuations in speckle patterns - which are directly related to the evolving structure of the material - reveal the activity caused by microstructural change. An ideal test material for developing our measurement technique is pure cobalt, which undergoes a martensitic phase transition between close-packed cubic and hexagonal crystal structures. Our measurements have revealed that during rearrangement between these structures, there is a series of fluctuations, or "microstructural avalanches", as cobalt heterogeneously transforms from the fcc to the hcp phase. These avalanches are caused by the sudden, collective relief of stresses on the lattice that have accumulated during the rearrangement of atoms. Using a wavelet-based detection scheme to analyze speckle patterns, the spatial and temporal characteristics of microstructural avalanches in cobalt were determined. These characteristics are analogous to those observed in a diverse collection of systems that exhibit heterogeneous dynamics, such as earthquakes.
10:15 AM - VV1.03
Microstructure Manipulation in Silicon-based Systems Using X-Rays
Conal E Murray 1 Sean M Polvino 2 I. C Noyan 2 E. Todd Ryan 3 Paul R Besser 4 Jean L Jordan-Sweet 1 Zhonghou Cai 5 Martin V Holt 5
1IBM T.J. Watson Research Center Yorktown Heights USA2Columbia University New York USA3GLOBALFOUNDRIES, Albany Nanotech Center Albany USA4GLOBALFOUNDRIES Sunnyvale USA5Argonne National Laboratories Argonne USAShow Abstract
Power densities generated by current generation synchrotron-based x-ray beamlines have attained sufficient levels to alter the microstructure within inorganic as well as organic materials, providing new opportunities to tailor their local properties. Within silicon-on-insulator (SOI) technology, submicron x-ray beams are capable of altering the crystallinity of the active silicon layer. The interaction region between the affected silicon and its surrounding environment extends to distances substantially larger than the incident beam footprint. Through in-situ and ex-situ investigations, we demonstrate that irreversible deformation generated in the underlying silicon oxide layer is responsible for modifying the local orientation of the SOI. A second example will be presented on the interaction of x-rays with dielectric / metallic nanocomposites, where alteration of the dielectric material can be used to impose stress within encapsulated copper structures. The time-resolved evolution of stress can be quantified in-situ using synchrotron-based x-ray diffraction techniques. We will discuss the interplay between the composite geometry and the amount of irradiation on the observed changes in stress of the copper features. These findings are compared to mechanical modeling to reveal two distinct modes of modification that the dielectric material undergoes: densification followed by an increase in elastic modulus.
10:30 AM - *VV1.04
Coherent X-Ray Diffraction Imaging: New Approaches to High Resolution Imaging
Keith Alexander Nugent 1 Brian Abbey 1
1The University of Melbourne Parkville AustraliaShow Abstract
New sources of X-rays are making ever more intense and coherent beams available to experimentalists. One important emerging area is known as coherent diffractive imaging (CDI) in which the diffraction from an object is used to form a high-resolution image of it without the need for additional X-ray optics. This method has been the subject of very significant development over the last decade or so and it has now been developed to the point where it can be applied to a number of important problems in materials science and a range of other areas. In this talk, I will review this method and some of its more important areas of application. An important motivation of CDI has also been its application to studies with the new X-ray free electron laser facilties. If time permits, I will describe some very recent experiments in which it is observed that materials diffract in rather different ways when subjected to extremely intense coherent ultrashort X-ray pulses.
11:30 AM - *VV1.05
Transformative Materials Science Enabled by an Energy Recovery Linac (ERL)
Joel D Brock 1 2
1Cornell University Ithaca USA2Cornell University Ithaca USAShow Abstract
The intense, highly collimated and spatially localized beams produced by an undulator on an Energy Recovery Linac (ERL) will approach the Fourier transform limit, ΔxΔk ge; 1/2, for localizing waves. To make contact between the wave description and the more familiar rays of geometrical optics, one makes the approximation Δkasymp;kΔtheta;. The uncertainty relation is then given by ΔxΔtheta; ge; lambda;/4π, which is known as the “diffraction limit” and places a fundamental constraint on how small the phase-space area (the product of the size and the angular divergence) of an x-ray beam can become. The ERL&’s x-ray beams are also almost fully coherent - that is, the contrast of fringes in interference experiments is approaching unity. The exquisite x-ray beams produced by an ERL source will enable experimenters to use the most highly collimated beam consistent with the small spot size they desire. The full spatial coherence will enable coherent imaging techniques to move beyond demonstration studies and become widely useful research tools. Thus, the ERL will open up new frontiers in materials research including: enabling coherent diffraction imaging of strain fields inside of nanoparticles; the determination of the atomic structure of buried volumes ranging in size from nanometers to microns; in operando studies of electrodes in working batteries, fuel cells, and electrophotocatalysts; and time-resolved studies with sub-picosecond resolution. In this talk, I will review the basic concept of an ERL and the anticipated properties of its x-ray beams. Then, I will give a few brief examples of frontier areas of materials research which will be opened up by an ERL.
12:00 PM - VV1.06
Progress of 3D Coherent X-Ray Diffraction Imaging at the Refurbished ESRF Beamline ID10
Federico Zontone 1 Yuriy Chushkin 1 Oleg Konovalov 1
1ESRF Grenoble FranceShow Abstract
In the frame of the upgrade of the European Synchrotron Radiation Facility the ID10 beamline went through a major reconfiguration in 2012. The old multi station based on the beam multiplexing via transparent diamond monochromators, previously known as Troika, has been replaced by a serial double-station setup operating in 50% time-sharing mode with independent fully optimized optics. The first station has a dedicated setup for liquid scattering experiments in various grazing incidence geometries while the downstream station has a longer hutch hosting experiments based on the scattering of coherent hard X-rays (8keV), with techniques such as X-ray Photon Correlation Spectroscopy for quantifying temporal fluctuations in slowly varying speckle patterns and Coherent X-ray Diffraction Imaging (CXDI) for retrieving the exact spatial arrangement of static disordered samples from coherent diffraction patterns. CXDI is a lens-less imaging technique based on the inversion of oversampled diffraction patterns via phase retrieval algorithms. The resolution is just determined by the highest scattering angle where the intensity can be measured and it is ultimately limited by the radiation damage. By using CXDI it is possible to image micrometric-sized bulk samples with nanometer resolution in their natural state, where electron microscopy cannot be applied without sectioning. In particular, there is a strong interest in the 3D imaging of frozen-hydrated biological objects. Here we present the tools available for 3D CXDI at ID10, the high precision sample stage and the MAXIPIX pixel detector with a new data collection strategy for increasing oversampling without compromising the resolution in real space. Finally we show the first successful 3D imaging at 50 nm resolution of a micrometric agglomerate obtained from the spontaneous self-assembly of Fe2P nanoparticles.
12:15 PM - VV1.07
Novel Multiplexing Techniques for Advanced Instruments at Long Pulsed Spallation Source
Margarita Russina 1
1Helmholtz Zentrum Berlin Berlin GermanyShow Abstract
The long pulse spallation neutron sources call for new experimental approaches to utilize the high power of the flux in the most efficient way. Novel multiplexing techniques, such as Repetition Rate Multiplication  and Wavelength Frame Multiplication  help to solve the main challenge in the instrument design at the future European Spallation Source: how to take full advantage of the high neutron peak flux and at the same time provide high instrumental flexibility. The underlying principle of multiplexing techniques is to use a set of monochromatic wavelengths or a set of wavelength bands coming from the same source pulse by means of mechanical chopper system. In this case the instrumental parameters, such as wavelength resolution, wavelength band, repetition rate are not any more determined by the source pulse parameters, but can be flexibly defined by the chopper frequency, speed and chopper pulse. With other words, multiplexing techniques, allow us to create instead of one long pulse a number of mini-pulses with variable frequencies and pulse lengths but with the same peak flux as original pulse. Introduced first at Los Alamos National laboratory in IN500 project , the methods have been recently experimentally implemented with the help of unconventional use of existing time-of-flight instruments at continuous reactor sources , . The experiments provide full proof of principle of these methods and show an enhancement of data collection rates by up to an order of magnitude. The application of the Wavelength Frame Multiplication (WFM) in diffraction was found to provide unrestricted capability for flexible pulse shaping for high and variable resolution at long pulse sources, overcoming the conventional wavelength band limitations due the source pulse parameters ,. The results show constant TOF resolution and unperturbed spectral distributions, fully comparable to the common single wavelength frame operation of pulsed source diffractometers, even for every single source pulse. Furthermore, we introduced and tested WFM application  using phase slewing, asynchronous pulse shaping chopper operation, which allows to avoid the problem of the frame "stitching" in the data treatment procedures. References: 1. F. Mezei, J. Neutron Res. 6 (1997) 3 2. F. Mezei, M. Russina, Advances in neutron scattering instrumentation, in: I.S. Anderson, B. Guerard (Eds.), Proceedings of SPIE, vol. 4785, 2002, p. 24. 3. M.Russina, F. Mezei, Nuclear Instr. and Methods, A604 (2009) 624 4. M. Russina, Gy. Kali, Zs. Santa, F. Mezei, Nuclear Instr. and Methods A654,(2011), 383 5. M. Russina, F. Mezei, Gy. Kali, Journal of Physics: Conference Series, 340(2012) 012018 DOI: 10.1088/1742-6596/340/1/012018
12:30 PM - *VV1.08
Phonon Spectroscopy Using Time-resolved X-Ray Diffuse Scattering
David Reis 1
1Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
We discuss the prospects of performing equilibrium and nonequilibrium phonon spectroscopy by time and momentum-resolved x-ray diffuse scattering. In particular, we present recent results on photo-excited semiconductors and semimetals using the x-ray pump-probe end station of the Linac Coherent Light Source, free electron laser at SLAC. With this source we were able to achieve few hundred femtosecond resolution at hard x-ray wavelengths, sufficient to follow nonthermal phonon emission at the Brillouin zone-edge, as well as to measure dispersion of acoustic phonons through much of the zone. Recent advances in the source and detectors will allow with much greater resolution and range in the near future.
Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV5: Phase Transformations and Chemical Processes I
Tuesday PM, November 27, 2012
Sheraton, 2nd Floor, Independence W
2:45 AM - *VV5.01
Advanced Materials Exploration Using Time-resolved High Energy X-Ray Diffraction and Imaging Techniques
Veijo Honkimaeki 1
1ESRF Grenoble FranceShow Abstract
The development of new advanced materials and devices such as fuel cells, organic solar cells, rechargeable batteries, catalytic materials, etc. involves many challenges. For example, the complexity of these heterogeneous devices can only be studied adequately by a combination of experimental methods, in order to reveal the interplay between the microscopic material properties and the macroscopic device performances. As the need for combining techniques has been instrumental in the development of electron microscopy it is seen as equally important for the evolution of hard x-ray synchrotron methods applied in-situ for studying both real devices under operating conditions and idealized model systems under precisely controlled environments. The properties of the high energy x-rays, and their use in the studies of liquids, crystalline, nanocrystalline and amorphous materials using reflectivity, imaging, small angle x-ray scattering, diffraction and auxiliary techniques are discussed. Some examples of the applications using these techniques in the fields of metallurgy and materials research are given.
3:15 AM - VV5.02
Electronic Structure of Ligand-stabilized Atomically Precise Gold Nanocluster Catalysts
Jing Liu 1 2 Sai Krishna Katla 1 2 Yaroslov. B. Losovyj 1 2 Soma Chattopadhyaya 3 4 Jeffrey T. Miller 5 Challa S.S.R. Kumar 1 2
1Louisiana State University Baton Rouge USA2Louisiana State University Baton Rouge USA3Argonne National Laboratory Lemont USA4Illinois Institute of Technology Chicago USA5Argonne National Laboratory Lemont USAShow Abstract
We present results from our investigations into the electronic structure of atomically precise ligand-stabilized Au13[PPh3]4[S(CH2)11CH3]2Cl2 (Au13 for short) and Au25(SCH2CH2Ph)18 (Au25 for short) catalysts for styrene oxidation. The synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS) revealed low coordination, different geometric arrangement (Au-Au contraction) and d-band vacancies in the ligand-stabilized Au clusters in comparison to bulk Au. Au13 has a higher first shell Au coordination number than Au25, while the size (average coordination number) of Au13 was found to be smaller than Au25. The ultraviolet photoemission spectra (UPS) reveal a trend of narrower d-band width and d-band apparent spin-orbit splitting and higher binding energy of d-band center position with decreasing size of Au cluster. The d-band hole population of Au13 was seen to be higher than Au25. The ligands not only act as stabilizer but also play an important role as electron acceptor for Au atoms. We propose that these differences in their electronic structure could be responsible for variations in their activity and selectivity.
3:30 AM - VV5.03
In situ Synchrotron X-Ray Investigation of the Formation of Ordered Array of Silver Nanoparticles during Thermal Decomposition of Silver Carboxylates
Boris Bokhonov 1 Marat Sharafutdinov 1 Boris Tolochko 1
1Institute of Solid State Chemistry, Siberian Branch Novosibirsk Russian FederationShow Abstract
In the present work we report the formation of self-assembled structures of silver nanoparticles arising directly during thermal decomposition of silver carboxylates with the general formula [Ag(O2CnH2n-1)]2. The formation of ordered periodic assemblies of silver nanoparticles occurs from oxidation of the anion, with residual anion also acting as the capping agent. Monodisperse silver nanoparticles rapidly self organize into stable structures on the order of 0.5-1 mu;, and are characterized by TEM and in situ synchrotron x-ray SAXS and WAXS data. The in situ synchrotron x-ray investigation shows the changes in the diffraction patterns of a series of silver carboxylates, [Ag(O2CnH2n-1)]2 with n = 10, 12, 14, 16, 18, 22, directly during heating. As the sample of silver carboxylates reaches 180°C, the intensity of the small-angle scattering peak at 2theta;=1.1° increases, and continues to increase as the temperature rises to 200°C. The in situ X-ray investigation of the thermal decomposition of silver carboxylates at the diffraction angles 2theta;= 32-46°, showed that from 180°C and above reflections of metallic silver appear in the diffraction patterns. The electron microscopic investigation of silver carboxylates decomposed thermally at the small-angle scattering maximum showed that the product is composed of silver nanoparticles ordered in a regular periodic structure. This structure was observed for all the silver carboxylates investigated in the present work. The size of the nanoparticles is 5.2nm ±0.1nm. Unlike the previous reports of the self-assembly of silver nanoparticles occurring during drying colloid solutions on solid substrates, we find that self-assembled structures can formed directly during the thermal decomposition of metal carboxylates. In this case the formation of ordered periodic assemblies of silver nanoparticles during thermal decomposition of silver carboxylates allows these structures to be obtained in large amounts without any additional operations, that is, directly from the thermal decomposition of long-chain silver carboxylates without additional capping agents, reducing agents or structure directing components.
3:45 AM - VV5.04
Isostructural Phase Transition between Two Ferroelectric Phases of (1-x)BiFeO3-(x)PbTiO3 and Its Consequences on the Phase Diagram
Shuvrajyoti Bhattacharjee 1 Dhananjai Pandey 1
1Indian Institute of Technology, Banaras Hindu University,Varanasi Varanasi IndiaShow Abstract
There is currently enormous interest in the study of magnetoelectric coupling in solid solutions of multiferroic BiFeO3 with other ABO3 perovskites with a view to break the spatially modulated incommensurate spiral spin structure of pure BiFeO3 by introducing disorder in the magnetic sublattice. Amongst the various solid solutions of BiFeO3, the multiferroic (1-x)BiFeO3-(x)PbTiO3 (BF-xPT) system shows a rich variety of magnetic and structural phase transitions. In this presentation, we concentrate on the results of the discovery of an unusual ferroelectric to ferroelectric isostructural phase transition and associated giant negative thermal expansion for the tetragonal compositions near the morphotropic phase boundary (MPB). We have recently shown that the room temperature ferroelectric tetragonal phase (T1) of BF-xPT for x=0.31 exhibits extremely large tetragonality (~18%) on account of a first order isostructural phase transition from a high temperature ferroelectric phase which is also tetragonal (T2) but with lower tetragonality and identical space group (P4mm) and the occupied Wyckoff positions. The T2 phase finally transforms into the paraelectric cubic phase at still higher temperatures. Using group theoretical considerations, we have shown that the observed atomic displacements associated with this isostructural phase transition correspond to specific irreducible representations of the P4mm space group at its Brillouin zone centre. Pronounced anomalies in the thermal displacement parameters at the T1 to T2 transition provide evidence for such a phonon mediated isostructural phase transition. The high tetragonality ferroelectric phase (T1) of BF-0.31PT shows the largest negative thermal expansion coefficient reported so far in the mixed BF-xPT system. The isostructural transition is found to persist for tetragonal compositions of BF-xPT upto x = 0.60. We have established the complete phase diagram of the BF-xPT system showing the existence of a rare critical point in any perovskite system at T ~ 677 K for x raquo; 0.63. We acknowledge collaborations with Professor Y Kuroiwa, Professor C Moriyoshi and Mr Kazuaki Taji in this work and financial support from DST. References:  S. Bhattacharjee, S. Tripathi, and D. Pandey, Appl. Phys. Lett. 91, 042903 (2007).  S. Bhattacharjee, V. Pandey, R. K. Kotnala, and D. Pandey, Appl. Phys. Lett. 94, 012906 (2009).  S. Bhattacharjee, A. Senyshyn, P. S. R. Krishna, H. Fuess, and D. Pandey, Appl. Phys. Lett. 97, 262506 (2010).  S. Bhattacharjee, K. Taji, C. Moriyoshi, Y. Kuroiwa and D. Pandey. Phys. Rev. B. 84, 104116(2011).
4:30 AM - *VV5.05
In-situ X-Ray Laue Microdiffraction Studies of Phase Transitions in Vanadium Dioxide Microcrystals
John D. Budai 1 Alexander Tselev 1 Jonathan Tischler 1 Sergei Kalinin 1 Andrei Kolmakov 2
1Oak Ridge National Laboratory Oak Ridge USA2Southern Illinois University Carbondale Carbondale USAShow Abstract
Laue x-ray microdiffraction at synchrotron facilities enables mapping of local microstructures and strain distributions with submicron spatial resolution and high angular resolution. In particular, we have developed focused, polychromatic/monochromatic scanning microbeam techniques for microdiffraction and microfluorescence measurements with spatial-resolution of ~400 nm at the APS beamline 34-ID-E. This facility has been used to investigate the 3D microstructure and mesoscale evolution in a wide range of materials ranging from individual nanostructures to bulk polycrystals. In this talk, we describe in-situ microdiffraction of internal microstructural and strain changes associated with the metal-insulator transition in individual vanadium dioxide (VO2) microcrystals. VO2 is a strongly-correlated electron material that exhibits a classic first-order phase transition from a high-temperature tetragonal (rutile) metal to a lower-symmetry monoclinic insulator near room temperature. Understanding how the structural and electronic transitions couple with each other has remained an active research topic for decades. Unstrained samples transform abruptly from the rutile metal to the monoclinic M1 insulating phase, while relatively small external stresses can stabilize related monoclinic M2 and triclinic T insulating phases. Recently-developed techniques for growing high-quality micro- and nano-crystals with well defined geometries has enabled direct studies of the connections between local strain, symmetry and phase behavior, including our in-situ x-ray microscopy studies. Using scanning x-ray Laue microdiffraction, we obtained spatially-resolved maps of the crystal structure (phase) and orientation as a function of temperature. In addition, by inserting a monochromator into the beam and measuring the energy for particular Bragg peaks, the lattice strain was mapped. We will describe how stresses induced either by the substrate or by electrical currents can affect the metal-insulator transition and lead to the formation of different self-organized patterns of coexisting phases. Research supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (JDB, JZT) by the BES Scientific User Facilities Division (AT, SK) and by the NSF (AK). XOR-UNI at APS 34-ID supported by DOE BES Scientific User Facilities Division.
5:00 AM - VV5.06
Small-angle X-Ray and Neutron Scattering Studies of Chemically-tailored Polymers for Regulating Biomembrane Function
Scott M. Brombosz 1 Soenke Seifert 1 Millicent Anne Firestone 1
1Argonne National Laboratory Lemont USAShow Abstract
The use of amphiphilic block copolymers as agents to modify cell membrane structure and function has been an area of increasing research interest. Of particular interest has been the use of commercially available amphiphilic triblock copolymers of PEOn-PPOm-PEOn, so-called Pluronics or Poloxamers. Numerous investigations have explored their use in a wide range of biomedical applications, including modifiers in drug delivery, in-situ generated implants, synthetic chaperones, barriers against bacterial adsorption, neuroprotective and restorative agents, and soft tissue injury treatments (including stroke and electrical / thermal burns). In our prior work, we have identified specific polymer architectures among this family of triblock copolymers that seal defects or that form anti-microbial barriers on cell surfaces. Specifically, Small-angle X-ray scattering studies permitted determination of the 1D electron density maps of the polymer associated with a model biological membrane. More recently, we have chemically modified these polymers with quorum sensing regulating groups (e.g., phosphate) and examined how introduction of these groups alters the polymers interaction with the lipid bilayer. Insights on the mode of insertion of the chemically modified polymer and how they influence membrane structure is provided using X-ray and neutron scattering. This work provides a strong foundation for a significantly larger effort coupling basic research on the physical principles of polymer architecture and their relationship to the association and function of cell membranes.
5:15 AM - VV5.07
HEXRD to Study Transformations Kinetics in Titanium Alloys
Moukrane Dehmas 1 Elisabeth Aeby-Gautier 1 Guillaume Geandier 1 Amico Settefrati 1 2 Benoit Appolaire 3
1Institut Jean Lamour Nancy France2Airbus Operations Toulouse France3ONERA Chatillon FranceShow Abstract
Understanding and further modeling of microstructure formation, i.e. transformation sequences and kinetics need in situ characterization to quantify the transformation kinetics as well as to get additional characteristic for the multiphase polycrystalline component. In situ characterization using high energy X-ray diffraction (ID15 ESRF) were realized in parallel to more conventional techniques (electrical resistivity or dilatometry) to characterize transformations in metastable Ti alloys. High energy allowed to analyze a consequent volume of the specimen, avoiding surface effects, and to increase the sensitivity and acquisition frequency for the diffraction patterns. Our contribution aims to highlight results that could only be obtained using the in situ characterizations. For the set up used, specimens were in rotation to increase the number of analyzed parent grains. Heating was achieved by a radiant furnace and cooling by gas blowing. A specific sample holder was realized able to measure the temperature by a thermocouple spot-welded on the surface, even for the specimen under rotation. This allowed to apply controlled thermal variations. The beam was monochromatic and Debye Scherrer rings were recorded in transmission on a 2D detector. Time for acquisition and read out was 3.5s. After calibration, Debye Scherrer rings were integrated integration to obtain I-2theta; diagrams that were analyzed using Rietveld method (Fullprof program). Different results will be given. At first, the influence of the thermal path on the transformation sequences will be shown. Notably, we will illustrate the formation of different metastable states for precipitation during ageing. A complex sequence occurred depending on the heating conditions. For some lower heating rate, hexagonal isothermal omega; formed at first. Additional peaks were also observed that could be indexed as peaks of a CFC structure. Increasing the time or temperature, an orthorhombic phase (α”) appeared while peaks corresponding to omega; and β2 vanished. It is worth mentioning that HEXRD clearly demonstrated the formation of a metastable orthorhombic phase that is never mentioned in TEM observations. In addition, the evolutions of FWHM will be shown and compared for different transformation conditions. For the higher transformation temperatures, the diffusive character of the transformation could explain FWHM variations in the parent phase. The variations observed for the lower transformation temperatures need to consider additional factors that affect the ray profiles (stress state for example).
5:30 AM - VV5.08
Recent Results at SNAP, the High Pressure Diffractometer at the SNS
Antonio M dos Santos 1 Christopher A. Tulk 1 Jamie J. Molaison 1 Neelam Pradhan 1
1Oak Ridge National Laboratory Oak Ridge USAShow Abstract
The SNAP instrument at the SNS is currently the most advanced neutron diffractometer dedicated to high pressure research. The operating power of the SNS, current at 1 MW - and projected to reach 1.4 MW in the medium term - allows not only a very fast data collection, but also the reduction of sample size, in some cases, to sub milligram amounts. The ability to place the detectors at variable 2-theta; scattering angle and to select the appropriate neutron wavelength bandwidth range allows for the fine tuning of the ideal resolution/intensity parameters for each experiment. Since this facility has been made available to the high pressure user community, a broad range of materials systems have been investigated, in the form of powders, glasses and single crystals. Here we will present some recent scientific results of research performed at SNAP, namely examples of compression mechanisms of amorphous solids, magnetic phase diagrams in lanthanides, phase competition in manganites and structural studies of clathrate hydrates. These examples will highlight how appropriate use of the SNAP capabilities can be used to optimize high pressure experiments. In addition, ongoing improvements and additions to the SNAP capabilities will be discussed, in particular the recent development through the Instrument Development Team of a new generation of Diamond Anvil pressure cells that allows data collected up to 50 GPa, a new frontier in high pressure neutron scattering.
5:45 AM - VV5.09
Visualize Phase Transformation of Materials by in-situ Time Event Neutron Diffraction
Ke An 1 Alexandru Stoica 1 Dong Ma 1 Harley Skorpenske 1
1Oak Ridge National Laboratory Oak Ridge USAShow Abstract
The advent of extremely high neutron flux, unique time event data acquisition and novel instrumentation at SNS open up new possibilities, especially for in-situ dynamic and kinetic studies. With the-state-of-art instrumentation and advanced data processing, the engineering diffractometer, VULCAN at SNS provides an entirely new approach to study time-resolved phenomena such as in-situ phase transformation under temperatures, stresses, or electrical charges, et al. In this talk, we will present the advanced capabilities by several great phase transformation studies with time scales ranging from minutes to sub seconds, including a demonstration measurement of transient phenomena of microseconds time scale. Details of this measurement methodology as well as its potential application in various scientific cases will also be presented.
VV4: Functional Materials and Local Order II
Tuesday AM, November 27, 2012
Sheraton, 2nd Floor, Independence W
9:30 AM - *VV4.01
Advanced PDF Methods for Complex Materials
Takeshi Egami 1 2
1University of Tennessee Knoxville USA2Oak Ridge National Laboratory Oak Ridge USAShow Abstract
The method of atomic pair-density function (PDF) has long been used to characterize the structure of glasses and liquids, which do not have long-range order, through x-ray and neutron diffraction. It is usually assumed that the sample is isotropic, and atomic distribution depends only on radial distances between atoms. For this reason it is also called the radial distribution function (RDF). However, the sample is not necessarily isotropic. For instance when a stress is applied and the sample undergoes elastic or plastic deformation it no longer remains isotropic. In this talk we discuss advanced PDF techniques, the anisotropic PDF method to characterize anisotropic materials, and the dynamic PDF method to describe local atomic and spin dynamics. In the anisotropic PDF method the three-dimensional PDF, g(r), and the structure function, S(Q), are expanded by the spherical harmonics. The anisotropic PDF, gml(r), is related to the anisotropic structure function, Sml(Q), through the spherical Bessel transformation. We show how this approach elucidated the atomic processes for elastic and anelastic deformation of metallic glasses. The lattice and spin dynamics of a solid are usually described in terms of phonons and magnons, whose dispersion can be observed in the dynamic structure factor, S(Q,omega;), measured by inelastic scattering. In strongly disordered systems such as liquids, however, phonons and magnons are strongly damped, and their dispersion cannot be easily seen in S(Q,omega;). In solids the phonon dispersion is determined by diagonalizing the dynamical matrix. However, in liquids the dynamical matrix itself is time-dependent, so the diagonalization does not lead to phonon eigen-state and strong localization ensues. The dynamic PDF (DPDF), g(r,omega;), is a Fourier-transform of S(Q,omega;) over Q, and describes local dynamics well. We show an example of DPDF for liquids which demonstrates super-localization of atomic dynamics in liquids.
10:00 AM - VV4.02
Multiscale Synchrotron-based Study of the Physics and Device Impacts of Metal-dislocation Interactions in Silicon Solar Cell Materials
David P Fenning 1 Mariana I. Bertoni 1 2 Volker Rose 3 4 Joerg Maser 3 4 Tonio Buonassisi 1
1Massachusetts Institute of Technology Cambridge USA2Arizona State University Tempe USA3Argonne National Laboratory Argonne USA4Argonne National Laboratory Argonne USAShow Abstract
Silicon solar cells are generally limited by inhomogeneous nanoscale defects scattered throughout the bulk material, especially in low-cost multicrystalline devices. The interactions of metal impurities with structural defects, such as grain boundaries and dislocations, limit electronic transport and can also result in low breakdown voltages and shunts. Synchrotron-based X-ray microscopy has proven successful at determining the elemental distributions and chemical states of second-phase metal precipitates at grain boundaries. However, characterization of dislocation-impurity interactions has proven particularly challenging, as dislocations are often tens of microns apart across the 15.6 cm x 15.6 cm wafer and are decorated with nanoscale second-phase metal silicides or atomic point defects. Techniques capable of bridging the 7 orders of magnitude of this characterization problem are few. Recent advances in zone plate optics and nanopositioning now provide smaller X-ray beam spot sizes. A state-of-the-art hard X-ray nanoprobe beamline with x-ray fluorescence imaging capability at the Center for Nanoscale Materials at beamline 26-ID (APS) now can achieve beam spot sizes < 50 nm, providing unparalleled XRF resolution while maintaining reasonable acquisition times. Using this nanoprobe, we show that the recombination activity of dislocations in mc-Si is strongly correlated with the presence of precipitated metals . Furthermore, we examine wafers in the as-grown state after crystallization and compare to fully processed sister wafers to evaluate when during device processing dislocations are decorated with metals. Our preliminary findings suggest more widespread dislocation decoration during solar cell processing rather than during crystallization. Overall, we demonstrate a non-destructive hierarchical approach that can map elemental composition with 25 nm steps at selected regions of interest on a centimeter-scale sample. The advances in X-ray spatial resolution and sensitivity make tractable a host of inquiries pertaining to defect engineering in energy science such as the metal-dislocation interactions in silicon.  M. I. Bertoni , D. P. Fenning , M. Rinio , V. Rose , M. Holt , J. Maser and T. Buonassisi, “Nanoprobe X-ray fluorescence characterization of defects in large-area solar cells” Energy Environ. Sci., 2011,4, 4252-4257
10:15 AM - VV4.03
Determination of the Impact of Water in Fuel Cells Using Neutron Imaging and Advanced Electrochemical Methods
Pierre Boillat 1 Pierre Oberholzer 1 Eberhard H. Lehmann 2 Gamp;#252;nther G. Scherer 1 Alexander Wokaun 3
1Paul Scherrer Institut (PSI) Villigen Switzerland2Paul Scherrer Institut (PSI) Villigen Switzerland3Paul Scherrer Institut (PSI) Villigen SwitzerlandShow Abstract
Neutron imaging has been increasingly used to study the behavior of liquid water in operating fuel cells [1-4]. In the last years, the necessary spatial resolution for cross sectional imaging was achieved, and several studies reported the observation of water in the different functional layers of the cell [5-7], including the porous media used for the fine distribution of gases. In particular, by using an anisotropic resolution enhancement approach, we demonstrated the possibility of imaging with an effective resolution of 20 mu;m and exposure times of 10 seconds , making the observation of transient processes possible. The single observation and quantification of liquid water is not sufficient to understand its impact on cell operation. For this purpose, advanced electrochemical characterization methods were developed and simultaneously applied to imaging. Recently, we reported the use of a novel method using short pulses of helox (21% O2 in He) and of pure oxygen for the direct measurement of mass transport losses . Here, we will present the results of our latest work using the combination of steady state and time resolved neutron imaging with advanced electrochemical methods, including the previously mentioned helox pulse analysis. The relation between liquid water accumulation and the electrochemical characteristics were studied using either standard cell structures (which include lateral and perpendicular transport) or so called 1D cell structures, in which the lateral transport is minimized. The latter allows meaningful comparisons to simple transport models, as a first step in providing a reliable determination of the impact of liquid water on cell operation. 1. A. Geiger, A. Tsukada, E. Lehmann, P. Vontobel, A. Wokaun, and G. Scherer, Fuel Cells 2, 92 (2002). 2. R. Satija, D. Jacobson, M. Arif, and S. Werner, J. Power Sources 129, 238 (2004). 3. N. Pekula, K. Heller, P. Chuang, A. Turhan, M. Mench, J. Brenizer, and K. Ünlü, Nucl. Instr. Meth. A 542, 134 (2005). 4. D. Kramer, E. Lehmann, G. Frei, P. Vontobel, A. Wokaun, and G. Scherer, Nucl. Instr. Meth. A 542, 52 (2005). 5. M. A. Hickner, N. P. Siegel, K. S. Chen, D. S. Hussey, D. L. Jacobson, and M. Arif, J. Electrochem. Soc. 155, B427 (2008). 6. S. Kim and M. Mench, J. Electrochem. Soc. 156, B353 (2009). 7. P. Boillat, G. Frei, E. H. Lehmann, G. G. Scherer, and A. Wokaun, Electrochem. Solid-State Lett. 13, B25 (2010). 8. P. Boillat, P. Oberholzer, A. Kaestner, R. Siegrist, E. H. Lehmann, G. G. Scherer, and A. Wokaun, J. Electrochem. Soc. , Accepted manuscript (2012).
10:30 AM - VV4.04
Intercalation and Retention of Carbon Dioxide in Synthetic Fluorohectorite Clay at near-ambient Conditions
Henrik Hemmen 1 Karin Rustenberg 1 Jon Otto Fossum 1 Tomas Plivelic 2
1Norwegian University of Science and Technology (NTNU) Trondheim Norway2MaAXIV Laboratory at Lund University Lund SwedenShow Abstract
We show using synchrotron as well as in-house x-ray diffraction methods that gaseous CO2 intercalates into the interlayer space of the synthetic smectite clay fluorohectorite at conditions close to ambient. The rate of intercalation is found to be dependent on the interlayer cation (Li+ or Na+ in this case), with about one order of magnitude increased rate in Li-fluorohectorite compared to Na-fluorohectorite. We further show that Li fluorohectorite is able to retain CO2 in the interlayer space at room temperature, which could have applications related to CO2 capture, transport and storage. De-intercalation starts occurring at temperatures exceeding 30 °C.
10:45 AM - VV4.05
Difference in Elastic Properties of CrB2 Determined by Microscopic and Macroscopic Measurements
Katsushi Tanaka 1 Satoshi Tsutsui 2 Norihiko L Okamoto 3 Haruyuki Inui 3 Alfred QR Baron 2 4
1Kobe University Kobe Japan2SPring-8 Sayo-cho, Sayo-gun Japan3Kyoto University Kyoto Japan4SPring-8 Sayo-cho, Sayo-gun JapanShow Abstract
CrB2 possess the hexagonal AlB2 structure which belongs to the spacegroup of P6/mmm. The compound exhibits para- to antiferro-magnetic transition at 88 K. By using a macroscopic measurement technique, that is, a conventional resonant ultrasound spectroscopy with a millimeter size mono-crystal, significant elastic anomalies have been observed just above the magnetic transition temperature. On the other hand, elastic constants determined by a microscopic measurement technique, that is, an inelastic X-ray scattering method (BL35XU, SPring-8, Japan) do not show any elastic anomalies at around the transition temperature. In order to explain the discrepancy, we have introduced a kind of so called ΔE effect resulting from a multidomain structure. If crystal lattice is slightly deformed by a spontaneous magnetostriction in the antiferromagnetic state, the symmetry of crystal lattice is lowered from hexagonal to monoclinic when the symmetry of magnetic structure is taken into account. By the lowering of the symmetry, six magnetic domains are generated in the antiferro magnetic state. When magnetic domain boundaries move to response to externally applied stresses, the mechanical deformation is absorbed by nonelastic deformations induced by the movement of magnetic domain boundaries. This multidomain model well explains all the experimental results obtained by both microscopic (X-ray) and macroscopic (ultrasound) measurements. The microscopic measurement is useful to obtain the true elastic properties of crystal lattice without effects coming from a multidomain structure.
11:30 AM - *VV4.06
The Interpretation and Analysis of Diffuse X-Ray Scattering
Richard Thomas Welberry 1
1Australian National University Canberra AustraliaShow Abstract
The sharp Bragg reflections that occur in diffraction patterns of all real crystals are used by conventional crystallography to deduce the average repetitive arrangements of atoms or molecules. Diffuse scattering, on the other hand, contains information about the deviations from the average (i.e., different types of disorder) and gives structural information on a length scale (~1Å - 1000Å) that goes well beyond that of the average unit cell. In many important materials, it is this extended range of structural information that is crucial in determining their unique or novel properties, rather than the average unit cell structure. For crystalline powders or nanoparticles this information is spherically averaged so that interpretation and analysis is significantly impeded. However for single crystals the full three-dimensional information is preserved with both orientational and distance information unambiguously accessible, offering perhaps the most definitive means of elucidating the nanoscale structure. Despite the fact that diffuse scattering is a powerful probe of local and nanoscale structural information the development of methods to interpret and analyze it has lagged well behind the development of conventional average structure determination. The reasons for this are, first, that diffuse scattering intensities are very much weaker than Bragg peaks, making the experimental observation vastly more demanding and time consuming. However, the advent of intense synchrotron sources and various kinds of area detectors means that this aspect of the problem is largely solved and it is now possible to obtain high quality three-dimensional (3D) diffuse scattering data relatively routinely. The second reason for the lag in development is that the sheer diversity of different types of disorder that occur in nature has made it difficult to formulate a solution strategy that will work for all problems. Although interpretation and analysis of diffuse scattering from single crystals remains a challenging problem many advances have been made. In particular the use of Monte Carlo (MC) computer simulation of a model structure has become a powerful and well-accepted technique for this purpose. The method consists of comparing diffraction patterns calculated from a computer model of the disordered structure with measured X-ray or neutron diffuse intensities. The advantage of the method is that it can be applied generally to all systems regardless of their complexity or the magnitude of the atomic displacements that might be present. The only limitation is the extent to which the MC energy can be made to provide a realistic representation of the real system energy. At one extreme a very simplified model may be useful in providing a qualitative demonstration of particular effects while at the other a quantitative and very detailed description of a disordered structure can be obtained.
12:00 PM - VV4.07
Recent Trends in Photoelectron Spectroscopy for Materials Research
Henrik Bergersen 1 John Ahlund 1 Robert Moberg 1
1VG Scienta AB Uppsala SwedenShow Abstract
Photoelectron spectroscopy (PES) is an excellent tool for material research due to the possibility to probe both electronic and geometric structure. PES provides direct access to the properties of novel materials. In this contribution we discuss some recent trends in PES and present state-of-the-art work within the different applications. Photoelectron spectroscopy went through a revolution in the 1990&’s, with the development of parallel angular detection using 2D detectors, a development that VG Scienta is proud to have contributed to. The possibility of simultaneous recording of Angular resolved PES (ARPES) spectra enables not only band structure measurements, but also X-ray photoelectron diffraction (XPD), depth profiling and standing wave spectroscopy. Recent examples of ARPES results will be given, including studies of super conductors, graphene, and topological insulators. Experiments done under normal surface science conditions (Ultra High Vacuum) are of limited use in some applications, e.g catalysis, due to the pressure gap problem. This motivates the study of systems at ambient pressures. Here we present a High Pressure Photoemission (HiPP) instrument developed in collaboration with Advanced Light Source (ALS). This instrument allows standard PES measurements as well as spatial and angle resolved spectra at HiPP conditions. Some recent results include spatially resolved investigations of solid oxide electrochemical cells (SOC:s) and electrochemical properties of junctions. We will also report on recent advances in constructing a new generation of instrumentation combining HiPP and Hard X-ray Photoelectron Spectroscopy (HAXPES). A novel electron analyser, designed for optimal transmission in combination with very efficient differential pumping, will be presented together with preliminary results.
12:15 PM - VV4.08
Aqueous Solution Structure of Methane by Small-angle Neutron Scattering
Monika A. Hartl 1 Mark A. Taylor 1 John C. Gordon 2 Rex Paul Hjelm 1
1Los Alamos Natl Lab Los Alamos USA2Los Alamos Natl Lab Los Alamos USAShow Abstract
Water/methane aqueous mixtures are important in the study and processing of wet natural gas as well as for understanding homogenous catalytic conversion of methane to methanol. Methane shows considerable non-ideal thermodynamic mixing properties. Presumably this is due to the formation of nanoscale structures in solution as a consequence of its hydrophobic character. Various nanostructures have been proposed, for example water cage structures surrounding a single methane molecule. However, there is no direct experimental evidence in the literature for methane solution structure. We performed small-angle neutron scattering (SANS) measurements of protonated methane in heavy water at 298 C and at 0.7 and 1.5 MPa, for which we designed and build a specialized gas-mixing cell. The SANS data follows the Debye-Bueche model of a randomly distributed two-phase system with a correlation length of about 255 Å at both pressures. The Porod invariant, on the other hand, gives Phi;(1-Phi;)Δρ2 of 0.38 and 2.6 1016 cm4 at 0.7 and 1.5 MPa, respectively. This result indicates that the volume fraction of the methane-rich phase, Phi;, and or the composition of the phase, determining the contrast, Δρ, is dependent on the pressure. These results show a previously undisclosed aqueous solution structure of methane on the nanoscale domain.
12:30 PM - VV4.09
X-Ray and Neutron Diffraction Studies of Semiconductors for Solar Water Splitting
Peter Khalifah 1 2 Limin Wang 1 2 Andrew Malingowski 1 Alexandra Reinert 1 Daniel Weinstein 1
1Stony Brook University Stony Brook USA2Brookhaven National Laboratory Upton USAShow Abstract
In the last decade, there have been extensive efforts to develop new complex semiconductors capable of absorbing visible light and using the absorbed energy to split water and renewably produce hydrogen fuel. While a great deal of effort has been devoted to characterizing the activity of these semiconductors, much less effort has been devoted to understanding their structures and elucidating structure-property relationships. A combination of neutron and synchrotron powder diffraction experiments have been used to correct the structure of some wolframite and pyrochlore materials important to this field, as well as to determine the structure of novel pyrochlore and closely related compounds that we have designed and synthesized for visible light (Eg < 3.0 eV) water splitting applications. Furthermore, neutron pair-distribution function experiments have been carried out to understand disorder, inhomogeneities, intergrowths, and stacking faults in some oxynitride perovskite and wurtzite phases in concert with DFT studies, including Monte Carlo and molecular dynamics simulations.
12:45 PM - VV4.10
Characterization of Spin-lattice Coupling in Ferromagnetic Shape Memory Alloys Using in situ Neutron Diffraction
Abhijit Pramanick 1 Xun-Li Wang 5 Xiaoping Wang 1 Ke An 1 Valeria Lauter 2 Christina Hoffmann 1 Alexandru D Stoica 1 Haile Arena Ambaye 3 Zheng Gai 4
1Oak Ridge National Laboratory Oak Ridge USA2Oak Ridge National Laboratory Oak Ridge USA3Oak Ridge National Laboratory Oak Ridge USA4Oak Ridge National Laboratory Oak Ridge USA5City University of Hong Kong Hong Kong ChinaShow Abstract
Ferromagnetic shape memory alloys (FSMA) are considered for next-generation sensors and actuators due to their large magnetic-field-induced strains (up to 10%) and stress induced changes in magnetization (up to 30%). So far, Ni-Mn-Ga alloys have shown the largest magnetic-shape-memory (MSM) effect at ambient temperatures. The MSM effect arises from a strong coupling between the order parameters that characterize the electron spins and the orientation of the crystal lattice. The coupling between the equilibrium crystallographic and magnetic structures of an off-stoichiometric Ni2Mn1.14Ga0.86 alloy were elucidated from the refinement of high-resolution single crystal neutron diffraction data, following a (3+1)-dimensional superspace formalism. Structural and magnetic changes under the application of mechanical stress and/or magnetic field were determined from in situ diffraction experiments with polarized and unpolarized neutron beams. Under a compressive stress, single crystalline Ni2Mn1.14Ga0.86 was shown to exhibit a maximum pseudoplastic strain of ~5.5% , which results from orthogonal reorientation of the crystallographic twins. A method to quantify the amount of twin reorientation from in situ neutron diffraction patterns is presented, which shows that a 5.5% macroscopic strain corresponds to a reorientation of ~85% of the twins. Reorientation of crystallographic twins in Ni-Mn-Ga can also occur by the application of a moderate magnetic field of 1 T. Using polarized neutron diffraction, we have studied the rotation of the electron spins which occurs simultaneously during the process of twin reorientation. Furthermore, the effects of mechanical constraint and temperature on magnetic-field-induced structural and magnetic changes are also discussed.
Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV7: Materials Microstructure I
Wednesday PM, November 28, 2012
Sheraton, 2nd Floor, Independence W
2:30 AM - *VV7.01
High Energy X-Ray Diffraction Microscopy: Direct Observation of 3D Materials Responses
Robert M Suter 1
1Carnegie Mellon University Pittsburgh USAShow Abstract
Spatially resolved diffraction of high energy (> 50 keV) monochromatic x-rays is used to non-destructively map microstructure inside of bulk polycrystalline materials. Tracking of structural responses to thermal and mechanical processes allows direct comparisons to computational models. Measurements spanning macroscopic volumes of the order of a cubic millimeter with micron scale resolution generate large, statistically significant data sets for such comparisons. Measurements are carried out at the 1-ID high energy beamline at the Advanced Photon Source. Near-field High Energy Diffraction Microscopy (nf-HEDM) uses a line focused beam to illuminate planar cross-sections of samples. A precision rotation stage in combination with a high resolution area detector placed 5 to 15 mm downstream of the sample allows imaging of diffracted beams. Large numbers of Bragg peaks from each sample volume element are imaged as the sample rotates through 180 degrees. Measurements at multiple sample-to-detector distances encodes the scattering angles and the position of origin within the sample of each observed peak. Volumetric measurements consist of 100 or more such layer measurements. Microstructures, in the form of a voxel based crystallographic orientation field, are reconstructed via high performance computing using a forward model simulation of the experiment and sample structure. Examples illustrating these measurements will include annealing studies of high purity aluminum and nickel and tensile deformation measurements of copper and zirconium. Computational feature extraction and tracking will be described. Far-field HEDM measurements will be briefly described. Far-field HEDM measurements will be briefly described. These use a large format area detector placed about a meter downstream of the sample. Elastic lattice strain tensors are determined for individual crystalline grains inside of polycrystalline samples. Current work aimed at integrating near- and far-field measurements will be described. Integrated reconstructions should yield maps containing both the orientation and strain fields at sub-grain length scales. Such microstructure descriptions spanning macroscopic volumes in successive sample states should aid in addressing problems such as fatigue and failure which are dominated by rare initiation events.
3:00 AM - VV7.02
Phase Specific Interface Interactions in Layered Phase-separated Multicomponent Alloys with 3D Laue Diffraction
R. I. Barabash 1 J. Budai 1 W. Liu 2 J. Tischler 2 H. Bei 1 O. M Barabash 3
1Oak Ridge National Laboratory Oak Ridge TN USA2Advanced Photon Source Argonne USA3The University of Tennessee Knoxville USAShow Abstract
The depth-dependent, as-grown and deformation-induced strain and dislocations partitioned through the interfaces in a two-phase layered NiAl-Cr(Mo) structure are directly measured at the mesoscale using 3D X-ray microdiffraction. It is demonstrated that in the as-grown, undeformed state, neighboring submicron Cr solid solution and NiAl eutectic lamellae (doped with ~3% Mo) form a hetero-interface with 180 degree rotation around a <112> pole. It is shown that the mechanical response to the indentation of a layered composite with alternating Cr(Mo)-NiAl lamellae is distinct from the response of single-phase materials. In the center of the indent, after the load is released, the NiAl lamellae are under compressive forward stresses (with the same sign as the indentation-induced compression) while Cr solid solution lamellae are under tensile back stresses (with opposite sign from the indentation load). Supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
3:15 AM - VV7.03
Stress, Texture and Grain Size Measurement with 2D Detectors
Bob B He 1
1Bruker AXS Madison USAShow Abstract
2D detectors, when used for stress, texture and grain size evaluation, have many advantages over the conventional 0D and 1D detectors. First, the measurement time is significantly reduced due to the large portion of the diffraction ring being measured at each exposure. 2D diffraction data has a large angular coverage in both 2theta and gamma directions. The algorithms to analyze 2D data must be able cover the diffraction intensity distribution in both the 2theta and gamma directions. The diffraction vector approach has been approved to be the genuine theory in 2D data analysis. The unit diffraction vector for all the pixels in the 2D pattern measured in the laboratory coordinates can be transformed to the sample coordinates. The vector components expressed in the sample coordinates can then be used to derive fundamental equations for many applications. The 2D fundamental equation for stress measurement governs the relationship between the stress tensor and the diffraction cone distortion. The fundamental equation for stress analysis with 0D and 1D detector is a special case of the more general 2D equation. The diffraction intensity variation along the gamma represents the texture of the sample. The unit diffraction vector in sample coordinates maps the intensity variation into the pole-figure. The diffraction vector distribution given by the incident beam and gamma range also defines an instrument window which determines number of diffraction spots on the diffraction ring corresponding to the grain size and size distribution. Experimental examples in the above applications are also given in this presentation. Reference: Bob He, Two-dimensional X-ray Diffraction, John Wiley & Sons, 2009
3:30 AM - VV7.04
Mechanical Stability of Retained Austenite Grains in TRIP Steels Studied by Synchrotron X-Ray Diffraction during Deformation
Romain Blonde 1 Enrique Jimenez-Melero 3 1 Lie Zhao 1 Jon Wright 2 Ekkes Bruck 1 Sybrand van der Zwaag 1 Niels van Dijk 1
1Delft University of Technology Delft Netherlands2ESRF Grenoble France3University of Manchester Manchester United KingdomShow Abstract
Low-alloyed TRIP-assisted steels belong to a new generation of advanced steels that combine high strength with good formability. At room temperature, the TRIP microstructure contains three phases: ferrite, bainite and retained austenite. The remarkable combination of high strength and ductility results mainly from the TRansformation Induced Plasticity (TRIP) effect, which involves the martensitic transformation of the metastable austenite. However, the relation between the stability of the retained austenite and the mechanical properties of TRIP steels is still not understood in detail. The martensitic transformation behaviour of the meta-stable austenite phase occurring in low-alloyed TRIP steels has been studied in-situ at different length scales during deformation at the beam line ID11 of the ESRF. We have correlated the macroscopic behavior of the material to the observed changes in the volume fraction and lattice parameter of the phases obtained from the powder analysis of the diffraction data. The load partitioning and the texture evolution during deformation have been investigated as a function of temperature and stress, together with their effect on the austenite transformation behavior. Moreover, the intense beam of high energy X-rays with micron size dimensions makes it possible to monitor individual grains in the bulk of the material, we have been able to monitor the transformation of individual austenite grains into the TRIP microstructure. The critical stress for the transformation is correlated to microstructural characteristics like the austenite grain size, carbon content and Schmid factor. Combining the experimental results of powder data and single grains makes it possible to understand the austenite stability under mechanical loading.
3:45 AM - VV7.05
Neutron Imaging Investigations of the Hydrogen Related Degradation of the Mechanical Properties of Zircaloy-4 Cladding Tubes
Mirco Karl Grosse 1 Stephane Valance 2 Juri Stuckert 1 Martin Steinbrueck 1 Mario Walter 1 Anders Kaestner 2 Stefan Hartmann 2
1Karlsruhe Institute of Technology Eggenstein-Leopoldshafen Germany2Paul Scherrer Institut Villigen SwitzerlandShow Abstract
The hydrogen uptake during operation, design basis loss of coolant accidents (LOCAs) and severe accidents (accidents beyond LOCA) results in a degradation of the mechanical properties of the nuclear fuel cladding tubes. This hydrogen related reduction of strength and toughness has high safety relevance for the reactor under service and transient conditions. The neutron imaging investigations were performed at the ICON facility at the Swiss neutron source SINQ (Paul Scherrer Institute Villigen, Switzerland). The non-destructive character of neutron imaging allows in-situ investigations of hydrogen uptake and relocation process in zirconium alloys. The strong contrast between hydrogen (very high total neutron cross section) and zirconium (very low total neutron cross section) provides the possibility to detect even small changes in the hydrogen concentrations. The hydrogen uptake during operation can results in the so called delayed hydride cracking (DHC). In material with subcritical tensile loading hydrogen diffuses in the strained region of the stress field above the tip of a crack. It reduces the strength and toughness of this area significantly. The crack can grow in this area. The stress field shifts ahead the newly formed crack tip and the hydrogen follows. First time resolved neutron radiography investigations of the hydrogen distribution in a yielded specimen were performed. The inhomogeneous hydrogen distributions in cladding tubes after LOCA result in brittle regions and influence the material hardness and the fracture appearance in the tensile. These distributions were visualized by neutron radiography and quantitative determined by means of neutron tomography. In severe accidents were higher temperature can occur compared to LOCAs the hydrogen uptake results in a shift of the alpha to beta zirconium phase transition. A reduction of the melting point and local meting below the expected temperature is the consequence.
4:30 AM - *VV7.06
Materials Science and Engineering Using Neutron and Synchrotron X-Rays
Axel Steuwer 1 2
1ESS AB Lund Sweden2NMMU Port Elizabeth South AfricaShow Abstract
Neutrons and synchrotron X-rays are complementary tools for the characterisation of (engineering) materials. The versatility of both types of radiation is demonstrated and reviewed using key experiments covering a range of length scales, from nano meters precipitates to bulk residual stress, and using a variety of techniques such as diffraction and imaging. An important aspect of the applications has always been the commercial exploitation of large scale neutron & synchrotron X-ray facilities, and the state of the art, as well as future potential is discussed.
5:00 AM - VV7.07
In situ Time and Scale Resolved Synchrotron X-Ray Imaging Applied to Materials Science
Eric Maire 1 Marco Dimichiel 3 Peter Cloetens 2 Luc Salvo 4 Sylvain Deville 5
1CNRS INSA Lyon Villeurbanne France2ESRF ID19 Grenoble France3ESRF ID15 Grenoble France4Grenoble INP Grenoble France5Saint Gobain CREE Cavaillon FranceShow Abstract
The most commonly used of the modern 3D imaging methods is probably X-Ray Computed Tomography (XRCT) because of its multimaterial, multiscale and non destructive character. Thanks to synchrotron sources, XRCT has recently seen important improvements in terms of temporal and spatial resolution that we have applied for understanding the evolution of the microstructure of materials under load. XRCT can indeed be coupled with in situ loading of the sample (in situ tension or compression, in situ heating, in situ freezing, etc...). The 3D image of the initial microstructure of the sample can, in a final analysis stage, be used as a direct input for a numerical simulation of the response of the material to the load, the results of which being directly comparable to the in situ experiments. This presentation will illustrate this combination of techniques and how we have used it in recent studies in order to understand the deformation of heterogeneous materials. On the one hand, we will focus on recent examples where we have used ultra fast imaging (one tomography scan every second with a voxel size of 1 µm) for analyzing the fracture of fragile materials. On the other hand, we will also show examples where a very high resolution (voxel size below 100 nm) has been used to observe very small details of the microstructure and its evolution during ex situ tensile tests.
5:15 AM - VV7.08
Neutron Imaging Methods Using Scattering Effects for Spatially Resolved Measurements
Burkhard Schillinger 1 Michael Schulz 1 Steven Peetermans 2 Helena Van Swygenhoven 3 Eberhard Lehmann 2
1Technische Universitamp;#228;t Mamp;#252;nchen Mamp;#252;nchen Germany2Paul Scherrer Institut Villigen PSI Switzerland3Paul Scherrer Institut Villigen PSI SwitzerlandShow Abstract
Neutron Imaging development has skyrocketed in the past few years. Coming from simple transmission images through computed tomography and stroboscopic imaging, current imaging methods are now exploiting scattering effects to gather spatially resolved information that could so far only be achieved in a spatially integrating mode by dedicated scattering instruments. The new imaging methods will not replace but complement current scattering instruments by determining inhomogeneities in scattering samples and determining regions of interest for further examination. Energy-resolved Bragg-edge scanning can now identify areas of stress and strain, dark field imaging with linear phase grids or macroscopic scatter grids create emission images of small angle scattering, and magnetic depolarisation imaging visualizes quantum phase transitions between ferromagnetic and paramagnetic states as well as spatial inhomogeneities and differences in transition temperatures within samples. The talk will give an overview about current research in neutron imaging methods at several European institutes, illustrated with specific examples.
5:30 AM - VV7.09
Strain Development during Thermal Treatment of Steel-based MMC by High Energy X-Ray Diffraction
Guillaume Geandier 1 Moukrane Dehmas 1 Elisabeth Aeby-Gautier 1 Mickael Mourot 1 Sabine Denis 1 Olivier Martin 2 Nikhil Karnatak 2
1Institut Jean Lamour Nancy France2Mecachrome Tours FranceShow Abstract
Developments of composites materials had begun in the 1970's. They aimed in improving mechanical properties due to the presence of reinforcement particles. The addition of particles in a matrix led to different modifications: considering the nature of the phases and the microstructure, we can mention interface reactivity between matrix and particles, changes in the chemical composition of the matrix and modified kinetics of microstructure evolution in the matrix (as compared to the matrix without particles); considering the mechanical aspects, thermal stresses may be generated due to the differences in expansion coefficients between the particles and the matrix, or any changes in the matrix leading to a phase transformation. In the present work, we studied the evolution of the phases and the behavior of a steel based MMC during thermal treatments, for which a phase transformation occurred on cooling. Experiments and numerical simulation are considered. In order to characterize the phase evolution and mechanical state in the composite during thermal treatment, in situ high energy diffraction was used to provide direct analysis of the transformation sequences in the steel-based matrix composite (MMC) reinforced with TiC particles. The MMC was elaborated by powder metallurgy. Evolution of the phase fractions of the matrix and TiC particles as well as the mean cell parameters of each phase were determined by Rietveld refinement from high energy X-ray diffraction made on beamline ID15B (ESRF, Grenoble, France). The experimental results show that the presence of TiC particles modified the kinetics of phase transformation of the matrix, as compared to a matrix with same composition, by favoring the transformation at higher temperature. Phase transformation of the matrix from austenite to ferrite and cementite is evidenced by following the mass fraction of each phase. Moreover, evolution of the cell parameters evidences a non-linear behavior clearly observed at the end of cooling and associated with thermal stresses. The difference in the coefficient of thermal expansion between matrix and TiC particle as well as the phase transformation during heat treatment induce a strong effect on the stress state of each phase. In order to analyze the evolution of stress in each phase during thermal treatment and principally the effect of the phase transformation of the matrix, micromechanical calculations were performed using finite element method. The calculations take into account the thermal stresses and the volume changes associated with the matrix transformation. After cooling, it was found to be in compression (negative mean stress) in the TiC particles and in tension in the matrix area around the TiC particles with low shear stresses in both phases. The tendencies measured from in situ synchrotron diffraction (mean cell parameters) matched well with the numerical estimates.
5:45 AM - VV7.10
Quantitative Imaging of Lattice Distortions in Epitaxial Semiconductor Heterostructures Using X-Ray Bragg Projection Ptychography
Stephan O. Hruszkewycz 1 Martin V. Holt 2 Conal E. Murray 3 John Bruley 3 Judson Holt 4 Ash Tripathi 5 Oleg G. Shpyrko 5 Ian McNulty 2 Matthew J. Highland 1 Paul H. Fuoss 1
1Argonne Nat Lab Argonne USA2Argonne National Laboratory Argonne USA3IBM T.J. Watson Research Center Yorktown Heights USA4IBM Semiconductor Research and Development Center Hopewell Junction USA5University of California San Diego San Diego USAShow Abstract
Nondestructively resolving structural subtleties in nanomaterials that come about due to intrinsic size effects and extrinsic boundary conditions is a challenge for which high-resolution x-ray microscopy is well suited. X-ray Bragg ptychographic imaging techniques have been under development that combine aspects of nanodiffraction and coherent imaging, yielding a robust imaging approach that is sensitive to lattice strain and is capable of sub-beam diameter resolutions. Here, we will discuss the details of coherent x-ray Bragg projection ptychography (BPP) - a structural imaging technique we developed for nondestructively studying nanoscale materials - and present results obtained by applying the technique to measure strain in Si-Ge prototype devices. We have reconstructed, with 16 nm resolution, profiles of lattice deformation in 65 nm thick Si0.8Ge0.2 epitaxial thin film structures grown on a patterned (001) silicon-on-insulator substrate. Two sources of lattice distortion were revealed in this nanoelectronic system acting at length scales from tens to hundreds of nanometers from feature edges. The x-ray results will also be compared to cross-sectional TEM measurements and elastic modeling predictions to confirm their consistency with BPP analysis.
VV6: Phase Transformations and Chemical Processes II
Wednesday AM, November 28, 2012
Sheraton, 2nd Floor, Independence W
9:30 AM - *VV6.01
In-situ Scattering Study of Precipitate Nucleation in Complex Materials
Xun-Li Wang 6 Alexandru D. Stoica 1 Dong Ma 1 Ling Yang 2 Zhongwu Zhang 1 3 4 C. T. Liu 5 Michael K. Miller 2
1Oak Ridge National Laboratory Oak Ridge USA2Oak Ridge National Laboratory Oak Ridge USA3Auburn University Oak Ridge USA4Nanjing University of Science and Engineering Nanjing China5City University of Hong Kong Hong Kong Hong Kong6City University of Hong Kong Hong Kong ChinaShow Abstract
Fundamental understanding of precipitate nucleation and growth is essential for controlling the microstructure induced by phase transformation. Quite often, phase transformations in complex materials, which are spatially heterogeneous and chemically multicomponent, occur concurrently at multiple length scale. Over the last decade, we have been focusing on developing a powerful combination of experimental methods, in-situ diffraction and small angle scattering and complementary real-space atom probe tomography, to probe and elucidate how nanoscale precipitates nucleate and grow. In this talk, we will discuss nucleation in two materials systems: bulk metallic glass and nanostructured steel. In the case of bulk metallic glasses, simultaneous diffraction and small angle scattering showed how short- and medium-range order parameters compete and synergize to form long-range order during nano crystallization [1-3]. In the case of nanostructured steel, sub-nanometer individual nucleation events were successfully imaged by atom probe tomography after small angle neutron scattering experiments provided initial clues of what to look for . MKM, XLW and ZWZ were sponsored in part by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Atom Probe tomography research (MKM, ZWZ) at the Oak Ridge National Laboratory SHaRE User Facility and the scattering work at Advanced Photon Source, Los Alamos Neutron Science Center, and Spallation Neutron Source were sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. 1. X.-L. Wang et al., "In-situ Synchrotron Study of Phase Transformation Behaviors in Bulk Metallic Glass Using Simultaneous X-ray Diffraction and Small Angle Scattering," Phys. Rev. Lett., 91, 265501 (2003). 2. L. Yang et al., “Nano-scale solute partitioning in devitrified bulk metallic glass,” Adv. Mat., 21, 305-308 (2009) 3. D. Ma et al., “Power-law scaling and fractal nature of the medium range order in metallic glasses,” Nat. Mat., 8, 30-34 (2009) 4. Z. W. Zhang et al., “From embryos to precipitates: a study of nucleation and growth in a multicomponent ferritic steel,” Phys. Rev. B, 84, 174114 (2011)
10:00 AM - VV6.02
The Study of the Electronic Structure and Local Structure of (AuAg)144SR60 Catalysts by X-Ray Absorption Fine Structure
Jing Liu 1 2 Sai Krishna Katla 1 2 Soma Chattopadhyaya 3 4 Chanaka Kumara 5 Amala Dass 5 Challa S.S.R. Kumar 1 2
1Louisiana State University Baton Rouge USA2Louisiana State University Baton Rouge USA3Argonne National Lab Lemont USA4Illinois Institute of Technology Chicago USA5University of Mississippi Oxford USAShow Abstract
The electronic structure and local structure of thiol ligand stabilized (AuAg)144SR60 nanoclusters was investigated by X-ray absorption fine structure (XAFS). By comparing the XAFS of (AuAg)144SR60 with bulk Au and Ag, a better understanding of the effect of ligand and Ag on the Au-Ag structure was obtained. The Au L3 edge X-ray absorption near edge structure (XANES) was used to examine the d-band character of Au, which is highly related to the electronic, magnetic and catalytic activities of Au. It was observed that the d band hole population of Au in (AuAg)144SR60 is higher than that of bulk Au. The Fourier transforms of Au L3 edge and Ag K edge extended X-ray absorption fine structure (EXAFS) provided the information of atomic structure of (AuAg)144SR60 cluster such as average coordination number and bonding lengths. The form of AuAg alloy core was confirmed by EXAFS. The S K-edge XANES revealed the (AuAg)-S interaction in the (AuAg)144SR60 cluster. The (AuAg)144SR60 catalysts were investigated in the catalysis of styrene oxidation.
10:15 AM - VV6.03
In situ Electrochemical X-Ray Absorption Spectroscopy of Mg Deposition
Timothy Sean Arthur 1 Per-Anders Glans 2 Masaki Matsui 1 Jinghua Guo 2 Fuminori Mizuno 1
1Toyota Research Institute of North America Ann Arbor USA2Lawrence Berkeley National Lab Berkeley USAShow Abstract
Electrochemical energy storage devices are key components for innovative power train systems such as PHV, FCHV and EV. Especially for a long-range EV, the energy density of the battery system is very critical. The battery system for the EV requires significantly higher energy density than that of state-of-art Li-ion battery (LIB). Therefore, a post-LIB system is very important as a future energy source for the EV. We believe the multivalent Mg based battery system may achieve higher energy density than LIB because a Mg-ion transfers two electrons resulting in an improved capacity. Mg metal is an ideal anode active material for a rechargeable Mg battery system because it shows very good cycle performance without the formation of any metallic dendrites. Recently, we have isolated the active species for Mg deposition through crystallization, [Mg2(mu;-Cl)3omicron;6(OC4H8)]+, but little is known about the mechanism for Mg deposition from this electrolyte. The electrochemical deposition of magnesium from [Mg2(mu;-Cl)3omicron;6(OC4H8)]+ has been monitored in situ with X-ray absorption spectroscopy (XAS). The utility of the cell was confirmed by XANES through a shift in the Mg K-edge after reduction of the electrolyte. Furthermore, the XANES and EXAFS regions data have been analyzed to probe the interface between the electrolyte and platinum working electrode. In situ measurements showed the presence of an additional Mg species besides the Mg dimer at potentials below Mg plating. The electrochemical XAS experiments establish a method to directly observe the reduction process from complex Mg electrolytes.
10:30 AM - VV6.04
SANS/WANS Time-resolving Neutron Scattering Studies of Polymer Phase Transitions Using NIMROD
Geoffrey Robert Mitchell 1 Daniel Bowron 2 Artur Mateus 1 Paulo Bartolo 1 Thomas Gkourmpis 3 Khamphee Phomphrai 5 Daniel Lopez 4
1Institute Polytechnic Leiria Marinha Grande Portugal2Science and Technology Facilitiy Council Didcot United Kingdom3Borealis Stenungsund Sweden4ICTP Madrid Spain5Mahidol University Bangkok ThailandShow Abstract
We use new neutron scattering instrumentation to follow in a single quantitative time-resolving experiment, the three key scales of structural development which accompany the crystallisation of synthetic polymers. These length scales span 3 orders of magnitude of the scattering vector. The study of polymer crystallisation dates back to the pioneering experiments of Keller and others who discovered the chain-folded nature of the thin lamellae crystals which are normally found in synthetic polymers. The inherent connectivity of polymers makes their crystallisation a multiscale transformation. Much understanding has developed over the intervening fifty years but the process has remained something of a mystery. There are three key length scales. The chain folded lamellar thickness is ~ 10nm, the crystal unit cell is ~ 1nm and the detail of the chain conformation is ~ 0.1nm. In previous work these length scales have been addressed using different instrumention or where coupled using compromised geometries. More recently researchers have attempted to exploit coupled time-resolved small-angle and wide-angle x-ray experiments. These turned out to be challenging experiments much related to the challenge of placing the scattering intensity on an absolute scale. However, they did stimulate the possibility of new phenomena in the very early stages of crystallisation. Although there is now considerable doubt on such experiments, they drew attention to the basic question as to the process of crystallisation in long chain molecules. We have used NIMROD on the second target station at ISIS to follow all three length scales in a time-resolving manner for poly(e-caprolactone). The technique provides a single set of data from 0.01 to 100Å-1 on the same vertical scale. We present the results using a multiple scale model of the crystallisation process in polymers to analyse the results.
10:45 AM - VV6.05
In-situ XPS and XRD Observations of Chemical Vapour Deposition of Graphene
Robert Weatherup 1 Raoul Blume 2 Carsten Baehtz 3 Bernhard Bayer 1 Piran Kidambi 1 Robert Schloegl 2 Stephan Hofmann 1
1University of Cambridge Cambridge United Kingdom2Fritz-Haber-Institut Berlin Germany3Helmholtz-Zentrum Dresden-Rossendorf Dresden GermanyShow Abstract
Chemical vapour deposition on transition metal catalysts is a highly promising method for producing high quality graphene across large areas to enable the widespread use of graphene in applications. The limited understanding of the growth mechanism(s) involved in chemical vapour deposition of graphene means that growth control remains rudimentary. This motivates our in-situ approach to develop an atomic scale understanding of graphene formation and thus enable rational optimisation of the growth process. We perform time- and depth- resolved high-pressure X-ray photoelectron spectroscopy (XPS) and in-situ time resolved X-ray diffraction (XRD) on polycrystalline transition metal catalysts films during hydrocarbon exposure at temperatures of ~300-700C, and during subsequent cooling.1 The use of synchrotron radiation [BESSY (Berlin), ESRF (Grenoble)] is critical in obtaining high-intensity X-rays with selectable energy to give the necessary time- and depth-resolution. We focus on graphene nucleation and graphene domain size in relation to the catalyst grain size distribution and the C chemical potential.2 Time-resolved XPS allows a detailed comparison of transient states prior to and during graphene formation and corresponding C/metal core level signatures. We thus reveal that graphene growth occurs isothermally on Ni, rather than just by precipitation on cooling and that dissolved C in to the catalyst subsurface plays an important role.3 Based on these in-situ measurements we present a coherent growth model for graphene formation on metal catalysts with finite C solubility and demonstrate that this is an effective tool in optimising larger-area graphene growth. (1) Hofmann et al. J Phys Chem C 2009, 113, 1648. (2) Weatherup et al. Nano Lett. 2011, 11, 4154-60. (3) Weatherup et al. ChemPhysChem 2012, (Early View).
11:30 AM - VV6.06
Elastic in situ Neutron Powder Diffraction at High Gas Pressures Using a Sapphire Single Crystal Cell
Holger Kohlmann 1
1Saarland University Saarbruecken GermanyShow Abstract
Reaction pathways in solid state reactions are often not well investigated and thus rational synthesis planning of new compounds is hardly possible. Identifying and characterizing intermediate phases by in situ studies can be very useful in this regard. In order to investigate time-resolved solid-gas reactions, in particular the hydrogenation of intermetallic compounds, we have constructed a gas pressure cell for elastic in situ neutron powder diffraction. It is based on the design of a sample holder for inelastic scattering  and consists of a sapphire single crystal tube with stainless steel endcaps. Using a single crystal as container material has got the advantage that Bragg peaks from the cell material can be avoided given a proper orientation of the cell, resulting in a cleaner background than amorphous (e. g. silica) or polycrystalline cell materials (e. g. metals). Sapphire has got additional benefits, such as high yield strength withstanding high gas pressures, chemical inertness, especially no hydrogen embrittlement, and optical transparency. Heating is achieved contactless by two lasers allowing temperatures up to 1300 K, while hydrogen (deuterium) gas pressure up to 30 MPa can be applied, enabling studies under controlled gas pressure and temperature conditions. The reaction pathways of the hydrogenation of intermetallic compounds could be examined up to 16 MPa hydrogen (deuterium) pressure and 700 K. For test cases such as palladium and LaNi5 the α-β transition was followed, allowing the elucidation of structural details, including occupation and thermal displacement parameters, by Rietveld refinement at all T-p conditions examined. In palladium rich intermetallic compounds in situ studies provided a very detailed picture of hydrogen induced atomic rearrangements, yielding a model with gliding of MPd3 layers as a probable reaction mechanism . This model was successfully applied for synthesis planning, yielding new metastable metal hydrides and intermetallic compounds [2, 3]. Further examples include the hydrogenation (deuteration) of Zintl phases and hydrogen (deuterium) induced decomposition of rare earth compounds . These investigations demonstrate the potential of the single crystal sapphire based gas pressure cell for in situ elastic neutron powder diffraction and testifies the importance of in situ investigations of reaction pathways in solid state research.  B. C. Chakoumakos, C. J. Rawn, A. J. Rondinone, L. A. Stern, S. Circone, S. H. Kirby, Y. Ishii, C. Y. Jones, B. H. Toby, Can. J. Phys. 2003, 81, 183-189  H. Kohlmann, N. Kurtzemann, R. Weihrich, T. Hansen, Z. Anorg. Allg. Chem. 2009, 635, 2399-2405  N. Kunkel, J. Sander, N. Louis, Y. Pang, L. M. Dejon, F. Wagener, Y. N. Zang, A. Sayede, M. Bauer, M. Springborg, H. Kohlmann, Eur. Phys. J. B 2011, 82, 1-6  H. Kohlmann, E. Talik, T. C. Hansen, J. Solid State Chem. 2012, 187, 244-248
11:45 AM - VV6.07
Probing Inert Anodes with High-energy X-Rays
Kathie McGregor 1 2 Matthew R Rowles 1 2 Mark J Styles 1 2 Ian C Madsen 1 2 Nicola V.Y. Scarlett 1 2 Graeme A Snook 1 2 Andrew J Urban 1 2 Daniel P Riley 3
1CSIRO Clayton Sth Australia2CSIRO Clayton Australia3ANSTO Lucas Heights AustraliaShow Abstract
To date, the development of inert anode materials for processes in high temperature molten salts has relied on the characterisation of samples removed from their operational environment at various pre-defined points of interest. This ex situ approach can be problematic, as conventional analysis techniques typically require some form of sample preparation, ranging from simply allowing the sample to cool, to more invasive procedures such as cutting and polishing. While any material examined outside of its operational environment will be altered to some extent, friable surface layers, crucial to the understanding of the failure mechanism, are at particular risk. Obtaining clear information about how these layers evolve during cell operation, without disrupting their structure, requires a quantitative in situ characterisation method. Due to the aggressive sample environment - molten calcium chloride at 950 °C - the in situ characterisation of inert anodes is difficult and requires a penetrating, high energy method. Consequently, synchrotron energy-dispersive X-ray diffraction (ED-XRD) techniques were used. The intensity of such advanced radiation sources allows data to be collected on the time scales necessary to observe reaction changes and investigate their kinetics. This paper describes (i) the results from studies of selected anode materials during an electrolysis reaction in molten salts at 950°C using ED-XRD data collected on the JEEP beamline at the Diamond Light Source synchrotron, and (ii) the purpose built sample cell required to achieve the measurements.
12:00 PM - VV6.08
in situ Neutron Diffraction Study of the Li[LiwNixMnyCoz]O2 Layered Oxide Compounds during Electrochemical Cycling
Haodong Liu 1 Christopher Fell 2 Lu Cai 3 Ke An 3 Shirley Meng 1 2
1University of California San Diego La Jolla USA2University of Florida Gainesville USA3Oak Ridge National Laboratory Oak Ridge USAShow Abstract
Layered oxides have been the workhorse for rechargeable lithium ion batteries for the last two decades. During the delithiation and lithiation processes, many complex phenomena including transition metal migration, phase transformations can happen and affect the electrochemical performance of the batteries. Combining neutron and synchrotron x-ray diffraction we can monitor the complex changes in layered oxides at different state of charge/discharge. In situ neutron diffraction patterns were collected on the time-of-flight diffractometer, VULCAN, at the Spallation Neutron Source (SNS) during electrochemical charge/discharge cycling of the lithium-excess layered compound Li[Li0.2Ni0.18Mn0.53Co0.1]O2 and stoichiometric layered compound Li[Ni1/3Mn1/3Co1/3]O2. In this work, single-layer pouch cells were built for in situ study, graphite was used as anode material. Dynamic changes in d-spacing help to explain the lithium de-intercalation mechanism in these two materials. Strong anisotropy shifting of the lattice parameters during the first cycle and following cycles is observed. The in situ experiment shows distinct lithium and transition metal (TM) migration mechanisms in these two sets of cathode materials.
12:15 PM - VV6.09
Nucleation, Growth and Structural Dynamics of Electrodeposited Bismuth Thin Films
Manuel Plaza 1 2 Xin Huang 1 2 Jun Young Peter Ko 1 2 Darren S. Dale 3 Joel D. Brock 1 2 3
1Cornell University Ithaca USA2Cornell University Ithaca USA3Cornell University Ithaca USAShow Abstract
Measuring surface/interface structure evolution on atomic length scales in real electrochemical systems remains a technical challenge. Developing techniques for this kind of characterization is crucial for understanding technologically important systems such as fuel cells, batteries and electrophotocatalysts where the surface layers of the electrodes -- which control the activity, performance and life of the final device -- evolve with time. Bismuth is a component of several intermetallic materials which oxidize small organic molecules  and it can be epitaxially electrodeposited on GaAs (110) [2,3]. Therefore, Bi/GaAs (110) is attractive as a model test system on which we can obtain critical experience with a well-posed physical system before we study more complex electrochemical systems. In this talk, we present the results from an in-situ (real-time) two-dimensional X-ray Diffraction (XRD) study of the electrodeposition of bismuth thin films onto GaAs (110). We carried out the experiments at the A2 line of the Cornell High Energy Synchrotron Source. Bismuth was deposited from an aqueous electrolyte containing 1mM of Bi2O3 and 0.25M of HClO4 at several potentials from -40mV to -200mV (versus Ag/AgCl) and the XRD patterns were collected on an area detector (incident beam of 30KeV). A detailed analysis of the nucleation process of the bismuth as a function of the potential will be discussed by means chronoamperometry (CA) and Atomic Force Microscopy (AFM). The CA curves show that at low potentials -- below -150mV--, the nucleation is progressive whereas beyond -150mV the nucleation is instantaneous. In both cases the mechanisms of nucleation is controlled by diffusion of the species towards the electrode. The crystal quality will be also discussed as a function of the applied potential with special attention to the evolution of the film orientation, strain and texture.  Y. Liu, M.A. Lowe, K.D. Finkelstein, D.S. Dale, F.J. DiSalvo, H. D. Abruña. “X-ray fluorescence investigation of ordered intermetallic phases as electrocatalysts towards the oxidation of small organic molecules.” Chemistry 16 (2010) Pages 13689-13697.  P. M. Vereecken, K. Rodbell, C. Ji and P. C. Searson, "Electrodeposited Bismuth Thin Films on n-GaAs (110)," Appl. Phys. Lett. 86, (2005) 121916  M. Plaza, M. Abuin, A. Mascaraque, M.A. Gonzalez-Barrio and L. Perez, “Epitaxial growth of Bi ultra-thin films on GaAs by electrodeposition” Mat. Chem. Phys. 134 (2012) Pages 523-530.
12:30 PM - VV6.10
Determining the Thresholds and Activities of Slip, Twinning, and Displacive Phase Transformations via High Energy Diffraction Microscopy
Joel Vincent Bernier 1 Nathan Rhodes Barton 1 Donald Boyce 2 Daniel Farber 3 Chantel Aracne 4
1Lawrence Livermore National Laboratory Livermore USA2Cornell University Ithaca USA3Lawrence Livermore National Laboratory Livermore USA4Lawrence Livermore National Laboratory Livermore USAShow Abstract
High Energy Diffraction Microscopy (HEDM) is a relatively new experimental technique that can provide an unprecedented level of detail for grain-resolved studies of polycrystalline materials. When applied to in situ thermo-mechanical processing experiments, it is possible to determine the activities and associated thresholds for individual dissipative mechanisms at the crystal scale, including slip, twinning, and displacive phase transformations. Results from three studies are presented: determination of critical resolved shear stresses and slip system activites in a Ti-7%Al alloy; observations of variant selection for tensile twinning in AZ31 magnesium alloy; and determination of the transformation mechanisms as well as variant selection for the high pressure αharr;ε phase transition in iron and the α→omega; phase transition in zirconium. We conclude with a brief discussion of the current state of HEDM, both in terms of the development of dedicated instruments at synchrotron user facilities as well as open source analysis software. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (LLNL-ABS-561863). Funding through the Laboratory Directed Research and Development program (10-ERD-053) is gratefully acknowledged.
12:45 PM - VV6.11
Structural Evolutions in the Chemical Transformation from Nickel to Nickel Phosphide Nanoparticle Revealed by X-Ray Absorption
Don-Hyung Ha 1 Liane M Moreau 1 Clive R Bealing 1 Haitao Zhang 1 Richard G Hennig 1 Richard D Robinson 1
1Cornell University Ithaca USAShow Abstract
X-ray absorption spectroscopy (XAS) is a powerful and versatile means to study structures of materials. When combined with other tools such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and density-functional (DFT) calculations, a nearly complete structural and morphological picture of a chemical trainsformation in nanoparticles can be assembled. Theses combined methods enable the determination of both amorphous and crystalline phases in nanoparticles during unique nanoscale chemical transformations. In this study we synthesized nickel and Ni-P nanoparticles using tri-n-octylphosphine (TOP) as a P source and examined the nanoparticle samples with x-ray absorption spectroscopy (XAS) to report on the differences between the phases. We use a combination of XAS, x-ray diffraction (XRD) to characterize long-range order, and ICP-OES to confirm stoichiometry to gain insight into the Ni-P nanoparticle structure. These structural characteristics are related to the corresponding nanoparticle properties using a combination of both theoretical DFT (density functional theory) calculations and SQUID. By probing the local atomic structure of nanoparticles, XAS reveal a significant P concentration in the Ni and NixPy nanoparticle samples while XRD results show contributions only from fcc Ni. We compare the long-range structural order of XRD and the short-range radial structure from EXAFS and determine that phases. The possibility of XRD amorphous phases should be considered when using XRD for nanoparticle characterization, particularly when highly reactive reagents such as TOP are used in synthesis. Undesired impurities may significantly affect nanoparticle structure, and, in turn, their functionality. Magnetic and catalytic properties are shown to be greatly affected by phosphorus contents : DFT calculations show magnetization losses in the Ni system, as well as in Fe and Co systems. The work was supported in part by the National Science Foundation under Award Number CHE-1152922 and by the DOE, Office of Basic Energy Science under Award Number DE-SC0001086.
Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV9: Materials Microstructure III
Thursday PM, November 29, 2012
Sheraton, 2nd Floor, Independence W
2:30 AM - VV9.01
SANS Investigation of the Molecular Behavior of Entangled Polymers in a Non-linear Rheological Domain
Eric J. Yearley 2 Leslie A. Sasa 1 Rex Paul Hjelm 1
1Los Alamos Natl Lab Los Alamos USA2University of Delaware Newark USAShow Abstract
Small-angle neutron scattering (SANS) measurements were carried out simultaneously with rheological measurements using the Los Alamos Neutron Science Center Neutron Rheometer with Couette geometry on melts of high molecular weight hydrogenated polystyrene mixed with deuterated polystyrene at different ratios. From the rheological data, it was found that the melts exhibited monotonic shear thinning with viscosity decreasing as the inverse of the shear rate, indicating that the shear rates were in the convective constraint release (CCR) non-linear domain. The SANS of the polystyrene melts showed increased anisotropy with increasing shear rate up to 10 Hz, indicative of chain extension along the shear direction. The anisotropy decreased at higher shear rates. These effects may be explained in part by the current tube theories and the role of CCR in non-linear rheological effects. However, it is not clear what, if any, the well-known wall slip phenomenon plays at higher shear rates.
2:45 AM - VV9.02
Laue Simulation from 3D Discrete Dislocation Dynamic Modelling for Dislocation Structures Analysis of in-situ Deformed Micro-pillar
Christophe Le Bourlot 1 Steven Van Petegem 1 Camp;#233;cile Marichal 1 3 Jochen Senger 2 Daniel Weygand 2 Helena Van Swygenhoven 1 3
1Paul Scherrer Institut Villigen PSI Switzerland2Karlsruhe Institute of Technology Karlsruhe Germany3Ecole Polytechnique Famp;#233;damp;#233;rale de Lausanne Lausanne SwitzerlandShow Abstract
Diffraction is a now centenary tool to study crystallographic structures, from macroscopic bulk polycrystalline to nano-structured material. It is well known that dislocations in crystals cause streaking and broadening of Laue peaks. However, the footprint of a dislocation in a diffraction pattern doesn&’t originate from the dislocation itself but rather from its long-range elastic strain field. In case of an ensemble of dislocations the diffraction signal reflects the complex interaction of such strain fields. Deriving dislocation structures from diffraction peak profile analysis is then very involved. To improve data analysis, we use some micro-mechanical simulations (from MD to crystal plasticity in FEM) as input data to a new Laue diffraction simulation model for studying directly the effect of particular and known dislocation ensembles on the diffraction pattern and peak profile. The Fourier Transform approach for diffraction modelling has been used in a new ray-tracing code, to take into account both size and shape effect. In this work we link this tool with a 3D Discrete Dislocation Dynamic simulations [1-2] to follow the evolution of Laue diffraction patterns compared with dislocation activities during the deformation of micro-pillars. Therefore any a priori hypothesis on the dislocation structure in our sample is eliminated. Different starting configurations (dislocation structures and boundary conditions) are investigated to explore the effect on the peak shape, during micro-pillar tensile/compression test. This method fills the missing link between a pure modelling approach  and a pure experimental one , and provides tools for a qualitative and quantitative analysis of white beam micro-Laue patterns in term of dislocation structures .
3:00 AM - VV9.03
Preventing Catastrophic Failure: Residual Stress Analysis on Unannealed and Stress Relief Annealed Liquid Ammonia Cargo Tank
Andrew Becker 1 Alan Russell 1 Scott Chumbley 1
1Iowa State University Ames USAShow Abstract
Neutron diffraction experiments were a key part of a two-phase project to measure stress corrosion cracking and other safety hazards in pressurized anhydrous ammonia tanks called nurse tanks. Over 200,000 nurse tanks are in use in the U.S., and several have exploded in recent years causing extensive property damage, injuries, and loss of life. In this project, neutron diffraction revealed the residual stress distributions around the welds used to assemble tanks at the manufacturing facility. These measurements (performed at the Los Alamos Neutron Science Center using the Spectrometer for MAterials Research at Temperature and Stress - LANSCE/SMARTS) showed that residual stresses are quite high in the heat-affected zone near the welds, nearing the yield point of the metal at the inner surface of the tank. Since tensile stress is a critical factor in predicting stress corrosion crack growth rates, these residual stress data allow prediction of tank lifetimes as a function of crack sizes and locations. Stress relief annealing of the entire tank after it has been welded during manufacture should increase tank safety and service life because residual stresses would be largely removed by annealing. Only two companies manufacture nurse tanks in the U.S. today, and both companies tentatively agreed during project meetings to anneal all tanks manufactured in the future if it could be demonstrated that annealing would substantially improve nurse tank safety. To this end a test tank was given a stress-relief anneal. Neutron diffraction demonstrated a dramatic decrease in the residual stress and thus an increase in the projected tank lifetime. The experiments used 41 in. diameter, 12 in. tall hoop sections taken from nurse tanks by cutting the tanks 6 in. on each side of the circumferential weld. The cutting process resulted in a maximum stress change (monitored with five 3-strain-gage rosettes on each tank) of 27 MPa at the weld surface. This is much smaller than the 350 MPa to -200 MPa residual stresses shown by neutron diffraction The hoop, radial, and axial strains were determined for 76 2mm x 2mm x 2mm regions across the circumferential weld in a 1966, 1986, and annealed 2012 nurse tank. Unstrained lattice parameter measurements (d-zero measurements) were taken by cutting a thin slice of the hoop that contained the scanned region and then cutting slots in this slice so that diffraction patterns could be taken from 4mm x 4mm x 6 mm unconstrained “teeth”. These d-zero measurements proved that the changes in lattice parameter were not due to chemistry variations near the weld. SMARTS was key to this research because the large count rates allowed 5- to 30-minute inspections per data point, neutrons could penetrate through the 2-20 mm of steel in the beam path, and the SMARTS sample stage has better than the necessary 0.5mm positioning accuracy.
3:15 AM - VV9.04
Influence of Plastic Deformation on the Rafting Behaviour in Single-Crystal Ni-based Superalloys: A Diffraction Study
Stephane Pierret 1 2 Steven Van Petegem 1 Thomas Etter 3 Alex Evans 4 Helena Van Swygenhoven 1 2
1Paul Scherrer Institut Villigen Switzerland2Ecole Polytechnique Federal de Lausanne Lausanne Switzerland3ALSTOM Baden Switzerland4Institut Laue Langevin Grenoble FranceShow Abstract
Superior mechanical properties of single-crystal (SX) Ni-based superalloys at high temperatures are achieved due to the optimization of alloying composition and the γ/γ&’ microstructure, which consists of high volume fraction of cubic γ&’ precipitates coherently embedded in the γ matrix. The two phases exhibit a small lattice parameter misfit δ (around 10-3) due to differences in composition. During service of the turbine blade, the combined influence of stress and elevated temperature induces the directional coarsening of the precipitates in a preferred direction (rafting) which can alter the mechanical properties of the alloy. The misfit and the plastic deformation introduced in the material during loading have been identified as the main parameters driving the rafting of the precipitates. For the first time, rafting is reported in engine-ready blades. Residual strains in a blade cooled from the solution heat treatment (SHT) are investigated with neutron diffraction supported by surfrace metrology and neutron tomography to insure the correct positioning of the neutron gauge volumes in the hollow internal structure of the blade. The measurements reveal the presence of large residual strains in the γ matrix in the area of the blade which exhibits a rafted microstructure in the engine-ready blade and corresponds with large misfit. The introduction of plastic deformation at this position is confirmed by TEM investigations of the microstructure. Where no rafting is observed, dislocations are not observed and both the γ lattice strain and misfit are much lower. Therefore the introduction of plastic deformation during the cooling after the SHT is believed to cause rafting during subsequent heat treatments. In addtition, the evolution of the misfit is followed in-situ during creep at high temperature using neutrons and X-rays diffraction in two alloys: a Re-free and a 3wt% Re-containing SX alloy. Simultaneously, the evolution of the mosaicity is measured during creep using an innovative experimental set-up at the X-ray diffraction beamline. These experiments reveal differences in the evolution of the misfit parallel and perpendicular to the applied stress. It reflects the decrease/increase of the internal stresses in the different γ matrix channels surrounding the cubic precipitates leading to rafting. The initial mosaicity of both alloys is rather small with a few tenths of degrees and describes the misorientation between neighbouring dendrites. Upon loading at 180MPa above 1000°C, the mosaicity decreases until the intensity maxima corresponding with each dendrite merge to form a broad single orientation region. At 950°C, the mosaic structure retains upon loading and is stable during creep deformation. The difference in mosaicity evolution between the different creep conditions is