Alexander Goncharov Carnegie Institution of Washington
Roberto Bini University of Florence
M. Riad Manaa Lawrence Livermore National Laboratory
Russell J. Hemley Carnegie Institution of Washington
PP1: Synthesis and Characterization
Monday AM, November 27, 2006
9:30 AM - **PP1.1
High-pressure Synthesis and Characterization of the Nitrides of Some of the Group 9 and 10 Transition Metals.
Jonathan Crowhurst 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
10:00 AM - PP1.2
Computation of Temperature-Pressure Phase Diagrams of High-Pressure Nitrides.
Peter Kroll 1 Show Abstract
1 Inorganic Chemistry, RWTH Aachen University, Aachen Germany
Advances in instrumentation of diamond-anvil-cells and multi-anvil-cells provided the environment for recent chemical syntheses of novel nitride compounds at high-pressure/high-temperature conditions. Motivated by the simultaneous discovery of spinel-type silicon nitride by experimental and computational methods  we set out to study more binary nitride compounds of main-group elements and transition metals [2,3].To access the full metal-nitrogen phase diagram at elevated temperatures and high pressure, hence, to locate the thermodynamical equilibrium between different oxidation states upon nitridation of a given metal M, entropy effects of nitrogen are the dominant source for the difference between enthalpy ΔH and free enthalpy ΔG. We propose an explicit scheme to include the fugacity of nitrogen based on thermochemical data to solve this obstacle .The combination of first-principle and thermochemical calculations let us predict the synthesis of a new high-pressure phase of Ta3N5 at about 27 GPa. Synthesis of WN2 becomes feasible at about 45 GPa. The scheme is also applied to phase diagrams of noble metal nitrides, PtN2, IrN2, and OsN2.A. Zerr, G. Miehe, G. Serghiou, M. Schwarz, E. Kroke, R. Riedel, H. Fuess, P. Kroll, R. Böhler, Nature 1999, 400, 340.P. Kroll, W. Schnick, Chem. Eur. J. 2002, 8, 3530.P. Kroll, Phys. Rev. Lett. 2003, 90, 125501.P. Kroll, T. Schroeter, M. Peters, Angew Chem. Int. Ed. 2005, 44, 4249.
10:15 AM - PP1.3
New Ferromagnetic Nitrides, CaN and SrN, and their ``Recipe".
Masaaki Geshi 1 , Koichi Kusakabe 1 , Hitose Nagara 1 , Naoshi Suzuki 1 Show Abstract
1 Graduate school of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
Synthesis of substances which do not exist in nature may have enormous potentialities of getting materials with excellent properties. Recent experimental reports of the synthesis of PtN and IrN have provided examples that we can synthesize the new materials using special experimental techniques. On the other hands, the reliability of standard first-principles calculations has been widely recognized and those methods have been very strong tool to predict physical and chemical properties of materials including characters of elements. Our aim is to design new materials and provide further the synthesis processes of the new materials based on theoretical techniques. Here we introduce new type of ferromagnets, CaN and SrN designed by the use of first-principles calculations and propose how to synthesize such materials. The structure of CaN and SrN is a rock-salt structure. These are half-metallic ferromagnets and the ferromagnetic state is very stable compared with antiferromagnetic and nonmagnetic states. The structural stability is checked by first-principles molecular dynamics simulations. Our synthesis scenario proposed here for the CaN is: first heating up α-Ca3N2 until it transforms to β-Ca3N2, and then compressing the β-Ca3N2 to over 50 GPa around which pressure the chemical reaction Ca3N2 →2CaN + Ca occurs. After this, cooling it down and decompressing it. We show the electronic and structural properties of the CaN and SrN and the enthalpy difference as functions of pressure between the β-Ca3N2 and the system 2CaN+Ca to show possibility of the realization of CaN.
10:30 AM - PP1.4
Synthesis of New and Advanced Materials under Pressure Using Laser and Resistive Heating.
Hyunchae Cynn 1 , Choong-Shik Yoo 1 , David Young 1 Show Abstract
1 , Lawrence Livermore National Laboratory, University of California, Livermore, California, United States
High pressure material synthesis under pressure recently has been a very active and productive field of research area, and accordingly draws a lot of attention with a hope of finding useful material properties among the products. We have seen high temperature material synthesis making headway when SHS (Self-propagation High-temperature Synthesis) technique promoting exothermic chemical reactions to synthesize advanced materials. In-situ high pressure and high temperature material synthesis provides advantages not only to make clean products but also viability to retain high pressure and/or high temperature phases at ambient conditions. The best known example of a meta-stable phase quenched and retained at ambient conditions is diamond, which is the hardest material ever known to mankind. Recently synthesized and identified polymeric CO2-V is also a good example of unexpectedly high bulk modulus and a temperature-quenched product at high pressure1. A diamond anvil cell synthesis coupling high temperature heating especially laser heating at high pressure allows manipulating pressure and temperature path to explore new and advanced materials in a wide range of pressure and temperature conditions. B-C-N triangle is recognized as a backbone for a synthesis of high strength material as well as initial starting components to synthesize transition metal compounds. It is important to recognize that high material strength which is often identified for a hard material should be distinguished from compressibility. However, it is practically useful to compare bulk modulus of starting metal components to search for super-hard materials as synthesized recently, PtN2 and IrN2.3There is a strong correlation between bulk modulus and atomic volume as shown in the figure of bulk modulus vs. atomic volume (data from D. Young, 1991). The choice of element to synthesize super-hard compounds, nitrides, carbides, and borides as well as oxides are predominantly among 5d transition metals, Os, Ir, Pt, Re, W including 4d elements with slightly smaller values of bulk modulus, Mo and Ru.5Reference: 1.Yoo, C.S., Cynn, H., Gygi, F., Galli, G., Iota, V., Nicol, M., Carlson, S., Häusermann, D., and Mailhiot, C. (1999) Phys. Rev. Lett., 83, 5527.2.Gregoryanz, E., Sanloup, C., Somayazulu, M., Badro, J., Fiquet, G., Mao, H.-K., and Hemley, R.J. (2004) Nature Materials, 3, 294.3.Crowhurst, J., Goncharov, A.F., Sadigh, B., Evans, C.L., Morrall, P.G., Ferreira, J.L., and Nelson, A.J. (2006) Science, 311, 1275.4.Young, D.A. (1991) Phase diagrams of the elements, University of California Press (Berkeley).5.Cynn, H., Klepeis, J.E., Yoo, C.S., and Young, D.A. (2002) Phys. Rev. Lett., 88, 135701.This work was preformed under the auspices of the U.S. Department of Energy by theUniversity of California, Lawrence Livermore National Laboratory, undercontract W-7405-ENG-48.
10:45 AM - PP1.5
A New Superhard Material : Osmium Diboride OsB2.
Mohamed Hebbache 1 , D. Zivkovic 2 , L. Stuparevic 2 Show Abstract
1 Materiaux et Phenomenes Quantiques, University of Paris 7, Paris France, 2 Department of Metallurgy, University of Belgrade, Bor
11:30 AM - PP1.6
Single-Crystals of a new Carbon Nitride Phase with all-sp3 Carbon.
Peter Kroll 1 , Ralf Riedel 2 , Paul McMillan 3 , Elizabetha Horvath-Bordon 2 , Reinhard Boehler 5 , Edwin Kroke 4 Show Abstract
1 Inorganic Chemistry, RWTH Aachen University, Aachen Germany, 2 Materials- und Geoscience, TU Darmstadt, Darmstadt Germany, 3 ) Solid State Chemistry, Christopher Ingold Laboratories, University College, London United Kingdom, 5 , Max-Planck-Institut für Chemie, Mainz Germany, 4 Inorganic Chemistry, Technische Universität Bergakademie Freiberg, Freiberg Germany
Considerable efforts have been made to realize the enigmatic carbon nitride, C3N4, proposed almost two decades ago. Despite many claims, however, no proof was provided for its existance. Its possible decomposition into gaseous species (NCCN and N2) and the thermodynamic stability of diamond and nitrogen are obstacles that have to be circumvented by chemical techniques.In order to synthesize a nitrogen rich carbon nitride, we started with a single source type precursor that provides alternating C-N units, a N:C ratio > 1.33, is free from impurities (O, S), and stable in air. Experiments using a laser-heated diamond anvil cell (LH-DAC) were performed over a broad pressure and temperature range. After laser heating for several minutes at pressures exceeding 27 GPa and we obtained transparent samples. Fortunately, we never observed the formation of diamond in our experiments. Using extended laser heating time we obtained single crystals of the new carbon nitride phase with up to 1.5 μm in size.Experimental (Raman, EELS, nano-SIMS, TEM) analysis was supported by extensive calculations of possible candidate structures and their properties (Raman, EELS). In a joint effort is became possible to merge all the data into one congruent picture and to solve the structure of a hydrogen-containing carbon nitride with all carbon tetrahedrally (“sp3“) coordinated.The novel compound exhibits a bulk modulus that exceeds that of β-Si3N4. More details of structure and its properties will be presented. Its synthesis marks a significant step towards the realization of C3N4.
11:45 AM - PP1.7
Does Osmium Carbide Exist? Ab initio Investigation.
Mohamed Hebbache 1 , D. Zivkovic 2 , L. Stuparevic 2 Show Abstract
1 Materiaux et Phenomenes Quantiques, University of Paris 7, Jussieu France, 2 Department of Metallurgy, University of Belgrade, Bor
12:00 PM - PP1.8
In Situ Studies of Ultra-Incompressible, Superhard Transition Metal Diborides Under High Stress Conditions.
Michelle Weinberger 1 , Jonathan Levine 1 , Hsiu-Ying Chung 3 , Abby Kavner 2 , Richard Kaner 1 , Sarah Tolbert 1 Show Abstract
1 Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, United States, 3 Mechanical Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Department of Earth and Space Sciences, University of California, Los Angeles, Los Angeles, California, United States
12:15 PM - PP1.9
Tape Casting Technique for Fabrication of Graded-Density Impactors for Tailored Dynamic Compression.
Louis Martin 1 , Jefferey Nguyen 2 , Jeremy Patterson 2 , Daniel Orlikowski 2 , Palakkal Asoka-Kumar 2 , Neil Holmes 2 Show Abstract
1 Mechanical Engineering, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Physics and Advanced Technologies, Lawrence Livermore National Laboratory, Livermore, California, United States
Recently, the use of graded density impactors for dynamic compression experiments has received increasing interest. These gas gun experiments have demonstrated complex loading paths which can last microseconds, and may be capable of bridging the timescales of existing static and dynamic compression experiments. A tape casting technique has been developed for fabrication of the impactors. In the technique, a series of tapes were prepared in the Mg-Cu system with compositions ranging from 100% Mg to 100% Cu. The tapes were characterized for their layer thickness, density, and sound wave velocity. Impactors were fabricated by punching individual layers from the tapes, stacking and laminating them, removing the organic matrix, and hot-pressing the laminated structure. The density profile is determined by the order in which the tapes are stacked in the laminate and is therefore highly flexible. The resultant thickness and average density of the impactors is consistent with the data for the individual layers. Impactors were characterized for uniformity by ultrasonic C-scan and white light interferometry. Dynamic compression experiments were performed on a two-stage helium gas gun using the graded density impactors. Results will be presented and shown to agree well with hydrocode modeling. Work performed under the auspices of the U.S. DOE at the University of California/Lawrence Livermore National Laboratory under contract W-7405-ENG-48.
12:30 PM - PP1.10
Bonding CVD Diamond to WC-Co by High Pressure - High Temperature Processing.
Naira Balzaretti 1 , Altair Pereira 2 1 , Sergio dos Santos 1 , Rafael Camerini 2 1 , João da Jornada 3 1 Show Abstract
1 Physics Institute, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil, 2 Engineering School, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil, 3 , INMETRO, Xerém, Rio de Janeiro, Brazil
Diamond coated cutting tools can be produced with CVD diamond technology, either by direct deposition of the diamond film over the substrate or by brazing a self-standing diamond film on the substrate through a high temperature (HT) treatment under vacuum. However, the improvement of the adhesion between the diamond film and the substrate represents a challenge for the development of technologic applications. In this work we investigate the use of high pressure-high temperature (HPHT) processing to bond CVD diamond and WC-Co substrates to produce high-performance diamond coated cutting tools. Traditionally, in the field of diamond tools for machinery applications, HPHT processing is used for synthesis of diamond powder or for the production of polycrystalline diamond compacts (PCDs) by sintering of diamond grains with the aid of a metallic binder. In the approach we are proposing, the advantages of using HPHT are related to processing of the tools in the thermodynamic stability range of the diamond phase and to the increase of the mechanical grip at the interface, by elimination of voids and induction of chemical interaction between diamond and WC-Co. Two kinds of samples were processed in the range 2.5 GPa-7.7GPa and 1000°C-1500°C: (a) self-standing CVD diamond films (400 μm thick ) just placed over WC-Co substrates; (b) thin diamond films (10-40 μm) grown directly over the WC-Co substrates after chemical removal of Co from the surface. The results revealed a marked improvement in the adhesion of self-standing films when compared to samples prepared by brazing at HT under vacuum. SEM images revealed the complete elimination of voids at the interface and a diffusion of Co to the interface region. Analysis by Raman spectroscopy shows that, for the sample prepared at 2,5 GPa at different temperatures, there was a partial graphitization of the diamond film, probably related to the presence of Co at the interface. This effect was not observed for processing above 4 GPa. A shear stress test was adapted to evaluate the adhesion and the results showed that, under stress, the failure started with the rupture of the diamond film itself instead of crack propagation at the interface. The mechanical grip induced by the HPHT treatment plays a major role in the adhesion improvement. For the samples where the diamond film was grown directly over the WC-Co substrate, the adhesion was evaluated by an indentation test and the results indicate an important improvement after HPHT treatment. The SEM images of the interface revealed that Co infiltrated back to the region where it was previously removed, decreasing the brittleness of that region. The results obtained for both kind of samples indicate that it is possible to take advantage of the HPHT plants already available around the world to produce, also, high-performance CVD diamond cutting tools.
12:45 PM - PP1.11
Synthesis and Characterization of NanoComposite Superhard Materials.
Yusheng Zhao 1 Show Abstract
1 LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
PP2: Disordered Systems
Monday PM, November 27, 2006
2:30 PM - **PP2.1
Transformations in Halogenide (AlCl3, ZnCl2) and Chalcogenide (AsS) Melts Under Pressure.
Vadim Brazhkin 1 Show Abstract
1 Disordered Matter, Institute for High Pressure Physics, Troitsk, Moscow region, Russian Federation
3:00 PM - PP2.2
Structure, Translational and Orientational Order of the Amorphous Ices.
A. Marco Saitta 1 , Thierry Strässle 2 , Stefan Klotz 1 , Franz Saija 3 , Paolo Giaquinta 4 Show Abstract
1 Institut Minéralogie Physique Milieux Condensés, Université Pierre et Marie Curie, Paris France, 2 Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen Switzerland, 3 Istituto per i Processi Chimico-Fisici, Sezione di Messina, CNR, Messina Italy, 4 Dipartimento di Fisica, Università di Messina, Messina Italy
3:15 PM - PP2.3
High-Pressure Phase Transformation Within Supercooled Liquids and Amorphous Solids.
Jeffery Yarger 1 , Emmanuel Soignard 1 , Erin Oelker 1 , Harish Bhat 1 Show Abstract
1 Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, United States
4:30 PM - **PP2.4
Phase Separation and Solidification of Fluid Phosphorus.
Yoshinori Katayama 1 Show Abstract
1 Quantum Beam Science Directorate, Japan Atomic Energy Agency, Sayo, Hyogo, Japan
5:00 PM - PP2.5
Melting Line of Materials Under Pressure.
Tadashi Ogitsu 1 , Eric Schwegler 1 , Giulia Galli 2 1 , Andrea Trave 1 , Alfredo Correa 1 4 , Stanimir Bonev 3 , Andrew Williamson 1 Show Abstract
1 Physics, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Chemistry, University of California at Davis, Davis, California, United States, 4 Department of Physics, University of California at Berkeley, Berkeley, California, United States, 3 Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada
5:15 PM - PP2.6
Tailoring the Properties of Silica Glass Using High Pressure Synthesis Routes.
Liping Huang 1 , John Kieffer 1 Show Abstract
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
5:30 PM - PP2.7
Silica under Pressure: Compression Mechanisms and Coordination Changes from First-Principles Calculations.
Andrea Trave 1 , David Prendergast 2 , Eric Schwegler 1 Show Abstract
1 Quantum Simulations Group, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Physics, University of California at Berkeley, Berkeley, California, United States
The densification behavior of silica (SiO2) in its many crystalline and amorphous phases has been the focus of many experiments and theoretical investigations, with the interpretation of several points still controversial.In particular, transitions from low-density structures, characterized by 4-fold coordinated Si atoms, to high-density structures, with 6-fold coordination, are strongly affected by hysteresis effects. This leads to the formation of a variety of metastable phases with atomic structures characterized by intermediate coordination states, including the possible presence of 5-fold Si coordination.Using first-principles molecular dynamics simulations we examine various phases of silica and provide theoretical estimates of measured spectroscopic features typical of different Si coordination states. Our results provide support to ongoing research using novel experimental techniques for the study of silica amorphous and crystalline phases under pressure.This work is performed under the auspices of the U.S. Department of Energy at the University of California / Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
5:45 PM - PP2.8
Hume-Rothery Rules for Primary Solid Solutions: Influence of High-pressure.
Igor Abrikosov 1 Show Abstract
1 Department of Physics, Chemistry and Biology (IFM), Linkoping University, Linkoping Sweden
PP3: Poster Session
Monday PM, November 27, 2006
Exhibition Hall D (Hynes)
9:00 PM - PP3.1
Microstructure and Mechanical Behaviors of Nano-polycrystalline Diamonds Synthesized by Direct Conversion Sintering under HPHT.
Hitoshi Sumiya 1 , Tetsuo Irifune 2 Show Abstract
1 Electronics & Materials R&D Laboratories, Sumitomo Electric Industries, LTD, Itami, Hyogo, Japan, 2 Geodynamics Research Center, Ehime University, Matsuyama, Ehime, Japan
High-purity nano-polycrystalline diamonds have been successfully synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures. Microstructure and mechanical behaviors of these nano-polycrystalline diamonds were investigated. TEM analysis revealed that the polycrystalline diamond synthesized from graphite at ≧15 GPa and 2300-2600 °C has a mixed texture of a homogeneous fine structure (particle size: 10-30 nm, formed in a diffusion process) and a lamellar structure (formed in a martensitic process). Results of indentation hardness tests using super-hard synthetic diamond Knoop indenter showed the polycrystalline diamond has very high Knoop hardness of 120-145 GPa. On the contrary, the polycrystalline diamonds synthesized from the non-graphitic carbons at ≧15 GPa and 1600-2000 °C have a single texture consisting of a very fine homogeneous structure (5-10 nm, formed in a diffusion process) without a lamellar structure. The hardness values of the nano-polycrystalline diamonds from non-graphitic carbons (70-90 GPa) are significantly lower than that of polycrystalline diamond from graphite. Microstructure investigation beneath the indentation of these nano-polycrystalline diamond revealed that the existence of lamellar structure and the bonding strength of the grain boundary have a decisive influence on the hardness.
9:00 PM - PP3.10
Ab initio Studies of Defects and Impurities in Cubic BN Under High Pressure.
Tian Cui 1 , Fubo Tian 1 , Zhiming Liu 1 , Zhi He 1 , Yanming Ma 1 , Guangtian Zou 1 Show Abstract
1 , National Lab of Superhard Materials, Jilin University, Changchun, Jilin Province, China
9:00 PM - PP3.11
Pressure-Induced Magnetic Phase Transitions in Pr1-xSrxMnO3 Manganites (x = 0.48 – 0.85).
Boris Savenko 1 , Denis Kozlenko 1 , Zdenek Jirak 2 , Victor Glazkov 3 Show Abstract
1 Frank Lab of Neutron Physics, Joint Institute for Nuclear Research, Dubna Russian Federation, 2 , Institute of Physics, ASCR, Prague Czech Republic, 3 , Russian Research Center “Kurchatov Institute”, Moscow Russian Federation
9:00 PM - PP3.12
Structural Transitions of an Al-Based Metallic Glass under High Pressure.
Jie Tang 1 , Lu-Chang Qin 2 , Xiaojun Gu 3 , Ke Lu 3 Show Abstract
1 Material Physics Division, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 3 , Institute of Metal Research, Shenyang China
9:00 PM - PP3.13
Electroplated and PVD Hard Ta and Cr on Fe Under Cyclic High Temperature and Pressure Operation.
Sabrina Lee 1 , Rong Wei 2 , Paul Cote 1 Show Abstract
1 Benet Labs, US Army ARDEC, Waterveliet, New York, United States, 2 Materials Engineering Dept, Southwest Research Institute, San Antonio, Texas, United States
For A723 steel cylinders under cyclic high temperature (~1400 Degree C) and high pressure (>700 MPa or 100 Ksi) operation, cracks are generally induced in the direction of high friction and firing damages in steel include formation of untempered martensite, gray layers (FeS and FeO), and white layers (fine grained austenite). When coated with 120μm electroplated hard Cr to protect against high temperature and pressure wear and erosion, cycle life of the component is greatly extended. Electroplated Cr exhibits excellent adhesion to substrate steel. However, aqueous electrochemical plating process generates toxic Cr VI, expensive and difficult to clean. As-deposited hard Cr has characteristic cracks which allow hot aggressive propellant gases to penetrate and erode the substrate. Analysis of after-fired steel cylinders electroplated with hard Cr showed extensive cracks in Cr and steel, grain growth and re-crystallization in Cr, thermal-mechanical damages, melting, and hot gas wash in steel. The component cannot achieve required cycle life for future projective launchers. Plasma-enhanced PVD (physical vapor deposition) process is being considered as a potential environmentally friendly process to replace electroplating of hard Cr in high temperature pressure vessels. Cr and Ta refractory metals have excellent thermo-mechanical-chemical properties. PVD films (10-90mm of Ta, Cr, and Ta/Cr) were deposited on steel using plasma-enhanced planar and cylindrical magnetron systems. Effects of increased ion bombardment on coatings hardness, phase, grain size, topography, microstructure, phase, residual stress, and adhesion strength were investigated. Our analyses include metallography, scanning electron microscopy, X-ray diffraction, Auger electron microscopy. Our adhesion tests include microscratch test, groove adhesion test, pulsed laser heating test to simulate high temperature, and vented combustor to simulate high temperature and high pressure operational environment.Plasma enhanced PVD films showed excellent adhesion to steel under microscratch and groove adhesion testing. In preliminary pulsed laser tests, we used 20 cyclic laser pulses of 2.5 and 5.0 msec, 1.1 J/mm2, incident on 90μm Ta on steel. Ductile PVD Ta showed no damages, no cracks, no interface delamination; minimal interface tetragonal Ta transformed to bcc Ta; substrate steel showed untempered martensite in heat affected zone. Further development of plasma enhanced PVD techniques to test Ta and Cr coatings for potential electroplated Cr replacement is planned.
9:00 PM - PP3.14
High Pressure Structural Phase Transition and Elastic Properties of MgX (X = S, Se, Te) Semiconducting Compounds.
Netram Kaurav 1 , Kamal Choudhary 2 , Dinesh Varshney 3 Show Abstract
1 Department of Physics, Institute of Science and Laboratory Education, IPS Academy, Indore, MP, India, 2 Department of Physics, Shri Vaishnav Institute of Technology and Science, Baroli, Sanwer Road, Indore, MP, India, 3 School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore, MP, India
9:00 PM - PP3.15
Ab-initio Studies of Phase Stability in High Pressure Bulk Aluminum.
Michael Tambe 1 , Nicola Marzari 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
The National Ignition Facility, when operational, is expected to probe the properties of matter at pressures far higher than what is currently reachable in shock gun or anvil cells experiments. Ab-initio techniques become especially handy to probe the properties of matter at such extreme conditions. In this work, we use density-functional and density-functional perturbation theory in the GGA-PBE approximation to probe the phase stability of aluminum at pressures reaching the relevant range of 1000-2000 GPa, paying particular attention at the role of inner core electrons at extreme pressures, and at symmetry breaking perturbations.
9:00 PM - PP3.16
In-Situ Scattering Studies of Methane Hydrate Formation under High Pressure.
Tadanori Koga 1 , Shahrukh Mallick 1 , Maya Endoh 1 , Miriam Rafailovich 1 , Devinder Mahajan 2 , Sushil Satija 3 Show Abstract
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Brookhaven National Lab, Upton, New York, United States, 3 , NIST, Gaithersburg, Maryland, United States
Gas hydrates are inclusion compounds in which small hydrophobic guest molecules or atoms are trapped in cages formed by a network of hydrogen bonded water molecules. Of special interest is methane hydrate, known as "burning ice", as it occurs in large amounts in the sediments of the worldwide oceans and in the arctic permafrost regions. Since the amount of carbon stored in these natural deposits is estimated to considerably exceed all known reserves of coal and oil, scientists expect that methane hydrate could power the world for centuries. However, few detailed experimental studies have been conducted to explore how and when molecular organizations occur during the formation process. Here we use an in situ neutron reflectivity (NR) technique to study the water/gas interface where methane hydrate starts to form because of proximity to sufficient quantity of methane gas. In order to mimic environmental conditions (0
9:00 PM - PP3.17
The Equation of State of Plastically Deformed Nitrides Under Uniaxial Stresses.
John Vassiliou 1 Show Abstract
1 Physics, Villanova University, Villanova, Pennsylvania, United States
9:00 PM - PP3.18
On the High-Pressure Behaviour of Titanium Hydride.
Patricia Kalita 1 , Stanislas Sinogeikin 2 , Kristina Lipinska-Kalita 3 , Thomas Hartmann 4 , Andrew Cornelius 1 Show Abstract
1 Department of Physics and High Pressure Sciences and Engineering Center, University of Nevada Las Vegas, Las Vegas, Nevada, United States, 2 Geophysical Lab, Carnegie Institution of Washington, Washington DC, District of Columbia, United States, 3 Department of Geosciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States, 4 , Harry Reid Center of Environmental Studies, Las Vegas, Nevada, United States
9:00 PM - PP3.2
Chromium Impurity States in Pb1-xGexTe Alloys under Pressure.
Evgeny Skipetrov 1 , Alexey Plastun 1 , Boris Kovalev 1 , Lyudmila Skipetrova 1 , Tatyana Topchevskaya 1 , Vasily Slyn'ko 2 Show Abstract
1 Faculty of Physics, M.V.Lomonosov Moscow State University, Moscow Russian Federation, 2 , Institute of Material Science Problems, Chernovtsy Ukraine
9:00 PM - PP3.3
High P-T Synthesis of Superhard Carbon Nitrides from Graphite-like Precursors.
Qixun Guo 1 , Yusheng Zhao 1 , Jianzhong Zhang 1 Show Abstract
1 LANSCE-LC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
9:00 PM - PP3.4
High-Pressure Studies of the Rotor-Stator Compound Cubane-C60.
Bertil Sundqvist 1 , Agnieszka Iwasiewicz 1 , Eva Kovats 2 , Sandor Pekker 2 , Istvan Jalsovszky 3 Show Abstract
1 Department of Physics, Umeå University, Umeå Sweden, 2 Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, Budapest Hungary, 3 Department of Organic Chemistry, Eötvös Lorand University, Budapest Hungary
9:00 PM - PP3.5
P-V Relation for Ar up to High Pressure.
Seema Gupta 1 Show Abstract
1 Physics, Agra College , Agra , U.P., India
9:00 PM - PP3.6
Pressure-induced Structural Changes and Phase Transformations in Some Oxides with Pyrochlore Structure.
Fuxiang Zhang 1 , Jie Lian 1 , Udo Becker 1 , Lumin Wang 2 , Rod C. Ewing 1 2 Show Abstract
1 Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States, 2 Nuclear Engineering & Radiological Sciences, The University of Michigan, Ann Arbor, Michigan, United States
The ordered pyrochlore with A2B2X6Y1 stoichiometry belongs to the Fd-3m space group. The A site (16c) is occupied by larger cations and is eight-coordinated, located within a distorted cubic polyhedron. The B site (16d) is six-coordinated and usually occupied by smaller cations such as Ti4+ and Zr4+ and located in a distorted octahedron of oxygen. The X anions occupy the 48f site with 2mm symmetry and coordinated to two B4+ and two A3+ cations; while Y anions occupy the 8a site with 43m symmetry and tetrahedrally coordinated with four A3+ cations. A symmetrically identical anion site 8b is systematically vacant, and is surrounded by four B4+ ions. Due to their special structural character, many pyrochlore compounds show very rich quantum phenomena at low temperatures. Some pyrochlore compounds have also potential applications in electrochemical and nuclear engineering. Many interesting structure-related properties have been found in pyrochlore compounds up to now. Substitution of cations in the pyrochlore will result in order-disorder phase transitions. Such a transition can also be driven by thermal treatment and ion irradiation. In addition, solid-state amorphization was found in some heavily irradiated pyrochlores. The structural changes and phase transformations of pyrochlore RE2M2O7 (RE=Nd, Sm, Eu, Gd, B=Ti, Zr and Hf) have been studied by in-situ Raman scattering and/or x-ray diffraction at high pressures up to 60GPa. Depending on the ratio of the cations radius, external pressure causes the order-disorder transition in pyrochlore (pyrochlore-to-fluorite) at pressures from 13GPa to 30GPa. With the increase of pressure, the pyrochlore (or defect fluorite) structure is not stable and a pressure-induced phase transition occurred. The high pressure phase may be a distorted fluorite structure with a monoclinic or orthorhombic unit cell. Upon release of pressure, the high pressure phase transforms to pyrochlore, cubic fluorite and amorphous. Some of the quenched samples are also analyzed by high resolution transmission electron microscopy.
9:00 PM - PP3.8
High Pressure and High Temperature Induced Polymeric C60 Nanorods and Their Photoluminescence Properties.
Bingbing Liu 1 , Yuanyuan Hou 1 , Lin Wang 1 , Guangtian Zou 1 , Agnieszka Iwasiewicz 2 , Bertil Sundqvist 2 Show Abstract
1 , Jilin University, National Lab of Superhard Materials, Changchun China, 2 Department of Physics , Umea University, Umea Sweden
9:00 PM - PP3.9
Development of HPHT Technology for Mass-production of New Super Hard Materials.
Takeshi Sato 1 , Naohiro Toda 1 , Hitoshi Sumiya 1 , Tetsuo Irifune 2 Show Abstract
1 Electronics & Materials R&D Laboratories, Sumitomo Electric Industries,LTD, Itami Japan, 2 Geodynamics Research Center, Ehime University, Matsuyama Japan
Alexander Goncharov Carnegie Institution of Washington
Roberto Bini University of Florence
M. Riad Manaa Lawrence Livermore National Laboratory
Russell J. Hemley Carnegie Institution of Washington
PP4: Dense Molecular Materials
Tuesday AM, November 28, 2006
9:00 AM - **PP4.1
Quantum Monte Carlo Simulations of Dense Hydrogen.
David Ceperley 1 , Carlo Pierleoni 2 , Kris Delaney 1 , Miguel Morales 1 Show Abstract
1 Physics & NCSA, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 , Universita di L'Aquila, L'Aquila Italy
9:30 AM - PP4.2
First-principles Study of the Effect of Helium on the Onset of Dissociation in Liquid Hydrogen.
Kyle Caspersen 1 , Francois Gygi 2 , Eric Schwegler 1 Show Abstract
1 Physics and Advanced Technologies Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Applied Science, Univeristy of California Davis, Davis, California, United States
9:45 AM - PP4.3
Hydrogen-rich Molecular Systems at High Pressures and Temperatures.
Alexander Goncharov 1 Show Abstract
1 , Carnegie Institution of Washington, Washington , District of Columbia, United States
Knowledge of the elastic, optical and vibrational properties of materials under extreme conditions of high pressure and temperature is crucial for interpreting the results of seismological and planetary observations, for materials science, and for improving our understanding of physics and chemistry at such conditions. In this talk I will present the results of Raman, infrared, and x-ray diffraction measurements of hydrogen, water, and hydrogen-water clathrates under conditions of high temperature and high pressure in the diamond anvil cell (DAC). High temperatures are generated by laser heating using a metal coupler. I will present the results of study of hydrogen to 50 GPa and 1500 K, water to 55 GPa and 1500 K, and hydrogen-water clathrates to 60 GPa and 1500 K. These studies give examples of novel phase transitions, unexpected chemical transformations and establish the behavior of interatomic interactions in molecular materials under extreme conditions. I thank the following individuals for contributing to this work: J. Crowhurst, N. Goldman, L. Fried, C. Mundy, J. Zaug, R. J. Hemley, E. Gregoryanz, C. Sanloup, M. Somayazulu, Y. Meng, N. Guignot, M. Mezour.
10:00 AM - PP4.4
Single-crystalline Atomic Nitrogen.
Mikhail Eremets 1 , Alexander Gavriliuk 2 3 , Ivan Trojan 1 3 Show Abstract
1 , Max Planck Institut fuer Chemie, Mainz Germany, 2 , A.V.Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr.59, 117333, Moscow Russian Federation, 3 , High Pressure Institute of Russian Academy of Sciences, 142092, Troitsk Russian Federation
10:15 AM - PP4.5
Quantum Monte Carlo Study of a Hydrogen Molecule Under Confinement.
Tian Cui 1 , Jinhua Wang 1 , Zhiming Liu 1 , Yanming Ma 1 , Guangtian Zou 1 Show Abstract
1 , National Lab of Superhard Materials, Jilin University, Changchun, Jilin Province, China
11:00 AM - **PP4.6
High-pressure Oxygen and Hydrogen Studied by Neutron Diffraction.
Igor Goncharenko 1 Show Abstract
1 , Laboratoire Leon Brillouin CEA-CNRS, Gif-sur-Yvette France
11:30 AM - PP4.7
High Pressure-High Temperature Reactions in Xenon-Chlorine System.
Maddury Somayazulu 1 , Steven Gramsch 1 , Russell Hemley 1 , Ho-Kwang Mao 1 Show Abstract
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
11:45 AM - PP4.8
Atomistic And Mesoscale Modeling Of The Response Of Molecular Crystals To Dynamical Loading.
Alejandro Strachan 1 , Eugenio Jaramillo 2 , Thomas Sewell 2 Show Abstract
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
12:00 PM - PP4.9
Theoretical Study of Solid Sodium Borohydrides Under Pressure.
Eunja Kim 1 Show Abstract
1 Physics, UNLV, Las Vegas, Nevada, United States
12:15 PM - PP4.10
Pressure-induced Phase Transformations in Li-based Complex Hydrides.
Raja Chellappa 1 , Dhanesh Chandra 1 , Stephen Gramsch 2 , Maddury Somayazulu 2 , Russell Hemley 2 Show Abstract
1 Chemical & Metallurgical Dept., University of Nevada, Reno, Reno, Nevada, United States, 2 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
Li-based complex hydrides such as LiAlH4 and LiNH2 are being considered as candidate materials for hydrogen storage due to their high gravimetric hydrogen content. In this study, high pressure in-situ Raman spectroscopy was performed to determine the pressure-induced phase transformations in LiAlH4 and LiNH2. Raman spectra were collected upto 7 GPa for LiAlH4 and upto 25 GPa for LiNH2. The analyses of Raman spectra of LiAlH4 revealed a phase transition at approximately 3GPa from the ambient pressure monoclinic α-LiAlH4 phase (P21/C) to a high pressure phase (β-LiAlH4, reported recently to be monoclinic with space group I41/b) having a distorted [AlH4] tetrahedron. Preliminary analyses of data on LiNH2 suggests a phase transformation at approximately 14 GPa from ambient pressure tetragonal (I -4)to an unknown structure. A discussion on the effect of pressure on various vibrational modes for these compounds will be presented.
12:30 PM - PP4.11
A Molecular Dynamic Study of Chemical Reactions ofSolid Pentaerythritol Tetranitrate at Extreme Conditions.
Christine Wu 1 , M. Manaa 2 , Laurence Fried 2 Show Abstract
1 Physics and Advanced Technologies, Lawrence Livermore National Lab, Livermore, California, United States, 2 Chemistry and Materials Science , Lawrence Livermore National Lab, Livremore, California, United States
12:45 PM - PP4.12
Higher Order Elastic Constants of Argon and Krypton Under High Pressure.
Suresh Goyal 1 Show Abstract
1 Physics, Agra College, Agra, Agra, U.P., India
PP5: Properties Under Extreme Conditions
Tuesday PM, November 28, 2006
2:30 PM - **PP5.1
On Correlated Electron Systems and 'simple' Metals at High Pressure.
Karl Syassen 1 Show Abstract
1 , MPI for Solid State Research, Stuttgart Germany
Experimental high pressure studies of crystalline phases take advantage of numerous recent developments in diamond-anvil-cell techniques. Major advances have occurred in microscopic analytical methods that utilize synchrotron x-ray radiation (diffraction and inelastic scattering), optical spectroscopy, and synchrotron infrared spectroscopy. The subjects of interest range from illuminating the interplay between subtle changes in atomic arrangements, electron delocalization, magnetism, and superconductivity in correlated electron systems to fundamental questions about phase transformations, crystal structure, and the nature of interatomic bonding in 'simple' $sp$-band metals. Some recent results will be highlighted in this presentation. The focus will be on structural and electronic properties of transition metal perovskites near the insulator-metal borderline and on the complex phase transition behavior of highly compressed (but still low-density) alkali metals.Work performed in collaboration with I. Loa, M. Hanfland, X. Wang, K. Kunc, A. Mermet, M. Krisch, G. Vanko, G. Monaco, and Y.-L. Mathis.
3:00 PM - PP5.2
Scenario of High Pressure Phase Transitions in Multiferroic BiFeO3.
Alexander Gavriliuk 1 , Viktor Struzhkin 2 , Igor Lyubutin 3 Show Abstract
1 , Institute for High Pressure Physics, Troitsk, Moscow region, Russian Federation, 2 , Institute of Cristallography, Moscow Russian Federation, 3 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
3:15 PM - PP5.3
Pressure Dependence of Electron Density Distribution of Dielectric KNbO3 Polymorphs by Maximum Entropy Method (MEM) Using Single Crystal Diffraction Study.
Takamitsu Yamanaka 1 , Yuki Nakamoto 2 , Kennji Ohi 1 Show Abstract
1 Earth and Planetary Science, Osaka University, Toyonaka, Osaka, Japan, 2 Research Center for Quantum Science and Technology under extreme conditions, Osaka University, Toyonaka, Osaka, Japan
3:30 PM - PP5.4
Synchrotron X-ray and Mössbauer Spectroscopy of Iron in Oxides Under High Pressure.
Viktor Struzhkin 1 Show Abstract
1 , Carnegie Institution of Washington, Washington, District of Columbia, United States
The strong electron correlations play a crucial role in the formation of a variety of electronic and magnetic properties of the transition metal oxides. In strongly correlated electronic materials many theoretical predictions exist on pressure-induced insulator-metal transitions, which are followed by a collapse of localized magnetic moments and by structural phase transitions . The high-pressure studies provide additional degree of freedom to control the structural, electronic, optical, and magnetic properties of transition metal oxides allowing to address both fundamental and applied questions in these materials. With the development of the high-pressure diamond-anvil-cell tecnique the experimental studies of such transitions are now possible with the advanced synchrotron techniques. In our studies, several synchrotron radiation techniques have been applied to perform the high-pressure experiments on iron oxides having different crystal structures. The cubic yttrium iron garnet Y3Fe5O12, multiferroic BiFeO3 crystals, trigonal rare-earth borate GdFe3(BO3)4, iron monooxide FeO, and Fe-Mg-O magnesiowüstite were studied under high pressures up to 200 GPa in diamond anvil cells. The single crystals enriched with Fe57 isotopes have been prepared for nuclear resonance measurements. The Mössbauer transmission and Mössbauer synchrotron (NFS) spectroscopy (including low-temperature NFS measurements down to 10 K), X-ray diffraction and the synchrotron high-resolution Kβ X-ray emission spectroscopy (XES), optical absorption spectroscopy, Raman scattering, electron microscopy, and electro-resistivity measurements have been performed.  R.E. Cohen, I.I. Mazin and D.G. Isaak, Science 275, 654 (1997).
3:45 PM - PP5.5
Magnetic Collapse and Insulator-metal Transitions in Some 3D Metal Oxides Under High Pressures.
Igor Lyubutin 1 , Alexander Gavriliuk 2 , Viktor Struzhkin 3 Show Abstract
1 , Institute of Crystallography, Moscow Russian Federation, 2 , Institute for High Pressure Physics, Troitsk, Moscow region, Russian Federation, 3 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
4:30 PM - **PP5.6
Experimental Studies at the Core-mantle Boundary Conditions.
Hokwang Mao 1 , Wendy Mao 2 Show Abstract
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 2 LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
5:00 PM - PP5.7
Ab Initio Study of the Composition Dependence of the Pressure-induced Spin Transitions in Rocksalt (Mg1-x,Fex)O and Perovskite (Mg1-x,Fex)SiO3
Kristin Persson 1 , Amelia Berta 2 , Gerbrand Ceder 1 , Dane Morgan 2 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, University of Wisconsin - Madison, Madison, Wisconsin, United States
Recent experimental results suggest that Fe undergoes a high-spin to low-spin transition in both the rocksalt and perovskite phases at lower mantle pressures. These spin transitions may have a profound impact on the properties of the lower mantle. In this work ab initio methods are used to calculate the Fe spin-transition pressures as afunction of Fe concentration in the rocksalt (Mg1-x,Fex)O and perovskite (Mg1-x,Fex)SiO3 structures. The results for the perovskite phase show that as the concentration of Fe increases, the transition pressure decreases. This is directly opposite to the trend observed for the spin transition found in rocksalt (Mg1-x,Fex)O. In rocksalt, the transition pressure decreases with increasing Mg content due to the chemical compression by the smaller Mg2+ compared to the high-spin Fe2+ ion. While the chemical compression effect also occurs in perovskite, the more complex structure allows for additional contributions to the energetics (e.g., octahedral tilting), which dramatically changes the spin transition trends with composition. We also show that the spin transition in both phases issignificantly driven by the volume difference between the high-spin and low-spin phases, rather than just changes in the electronic structure with pressure.
5:15 PM - PP5.8
Multiscale Simulations of Iron at High Pressures and Temperatures.
Ronald Cohen 1 , Xianwei Sha 1 Show Abstract
1 , Carnegie Institution of Washington, Washington, District of Columbia, United States
5:30 PM - PP5.9
Pressure Response of the Ultraviolet Photoluminescence of ZnO and MgZnO Nanocrystallites.
Jesse Huso 1 , John Morrison 1 , Heather Hoeck 1 , Xiang-Bai Chen 1 , Leah Bergman 1 , Slade Jokela 2 , Matthew McCluskey 2 Show Abstract
1 Department of Physics, University of Idaho, Moscow, Idaho, United States, 2 Department of Physics, Washington State University, Pullman, Washington, United States
ZnO and MgZnO alloys are promising next-generation wide-bandgap semiconductors for optoelectronic applications, and also of considerable interest from a fundamental viewpoint. The environmentally friendly chemical composition and the deep excitonic level ~ 60 meV of ZnO make it an excellent candidate for high-efficiency ultraviolet light sources. Moreover, the MgZnO solid solution has been recently realized for thin films as well as for nanopowders. These optical alloys enable the tuning of the bandgap and the luminescence at the range of ~ 3.0 for ZnO of the wurtzite structure up to ~ 7 eV for the MgO of the rocksalt structure. The optical properties of bulk and nanoscale ZnO at ambient conditions have been extensively investigated. In contrast, less is known about their properties under the influence of applied pressure and still less so for ZnO nanomaterials. We present studies on the pressure response of the ultraviolet photoluminescence of ZnO and MgZnO nanocrystallites of size ~ 30 nm and of the wurtzite structure. We found that up to 6 GPa the pressure coefficients of ZnO and MgZnO (10% Mg) are 23 and 27 meV/GPa, respectively. The pressure coefficient of the ZnO nanocrystallites is similar to that reported elsewhere for bulk ZnO material. The higher value found for MgZnO is discussed in terms of the difference in the atomic numbers of the cation constituents. Additionally, the volume deformation potential was derived from the experimental results, and we found it to be -3.40 eV for the ZnO nanocrystallites, and -4.03 eV for the MgZnO nanoalloy. Moreover, results concerning the optical properties at pressure regimes higher than 6 GPa are presented as well.
5:45 PM - PP5.10
PbSe Nanocrystal Quantum Dots at High Pressures: Competition Between Bulk and Confinement Effects
Jeffrey Pietryga 1 , Richard Schaller 1 , Kirill Zhuravlev 1 , Robert Sander 1 , Victor Klimov 1 Show Abstract
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Semiconductor nanocrystal quantum dots (NQDs), nanometer-scale crystals of semiconductor materials, are the subject of intensive research because of their unique optical and electronic properties. These properties can differ markedly from those of the corresponding bulk material, but often arise from a combination of both bulk and size-dependent contributions. For instance, the optically observed band gap of lead selenide (PbSe, bulk band gap = 0.26 eV) NQDs can be tuned over the range of 0.3 to 1.5 eV by reducing particle diameter from 17 nm to < 2 nm, as the quantum confinement energy contribution increases with decreasing particle size.1
The interplay of bulk and size-dependent properties in NQDs can be especially interesting at high pressures. This is particularly true in small PbSe NQDs with large confinement energy, a technologically important material with bright, narrow emission in the telecom band at 1.55 μm. The band gap of bulk PbSe is known to decrease with pressure (i.e. the deformation potential is negative2), resulting in a red-shift of the absorption edge with increasing pressure. However, application of high pressures to PbSe NQDs results in reduction in volume, according to the material compressibility, with a concomitant rise in confinement energy. This should result in a blue-shift of the absorption edge, essentially competing with the contribution from the deformation potential. Complicating the balance are the possible size-dependence of compressibility, and the non-linearity of confinement energy with size.3
We have carried out a series of optical and powder x-ray diffraction4 experiments designed to elucidate the relative contributions of these numerous, often competing interactions. Using a diamond anvil cell, we have studied a range of sizes of colloidal PbSe NQD in solution under pressures from ambient to more than 4 GPa. These studies reveal a system that, while dominated by bulk properties, has a significant size-dependent contribution from confinement energy. In addition, we have been able to educe fundamental insights through correlations of size, temperature and pressure dependencies of the band gap energy. We will present the results of our studies, as well as a discussion of fundamental and applied aspects of this research.
References and notes:
1. Pietryga, J.M.; Schaller, R.D.; Werder, D.; Stewart, M.H.; Klimov, V.I.; and Hollingsworth, J.A., J. Am. Chem. Soc., 126(38), 11752 (2004).
2. Rached, D.; Rabah, M.; Benkhettou, N.; Driz,M.; and Soudini, B., Physica B 337, 394 (2003).
3. Allan, G. and Delerue, C., Phys. Rev. B 70, 245321 (2004).
4. Synchrotron XRD pattern collections were performed at the Advanced Photon Source at Argonne National Laboratory.