Symposium Organizers
John Durrell, University of Cambridge
Luisa Chiesa, Tufts University
Kazumasa Iida, Nagoya University
Takanobu Kiss, Kyushu University
Marina Putti, Università di Genova
Symposium Support
ESAS European Society for Applied Super Conductivity
JECC TORISHA Co., Ltd.
Research Institute of Superconductor Science and Systems, Kyushu University
EP13.1: Tailoring Materials I
Session Chairs
John Durrell
Takanobu Kiss
Tuesday PM, March 29, 2016
PCC North, 200 Level, Room 226 B
2:30 PM - *EP13.1.01
From Dust to Devices: Focused Ion Beam Microfabrication for Superconductor Research
Philip Moll 2,Bertram Batlogg 2,Hai-Hu Wen 3,Peng Cheng 3,Xiyu Zhu 3,Nikolai Zhigadlo 2,Janusz Karpinski 2,Luis Balicas 4
1 Max Planck Institute Dresden Germany,2 Solid States Physics ETH Zurich Zurich Switzerland,2 Solid States Physics ETH Zurich Zurich Switzerland3 Institute of Physics Nanjing University Nanjing China4 Florida State University Tallahassee United States
Show AbstractWhenever novel classes of unconventional superconductors such as the iron-arsenides are discovered, initial research struggles with the complications arising from the often complex chemistry. The first samples rarely are high quality single crystals, but powders or poly-crystals commonly suffering from off-stoichiometry and parasitic phases. Here we present an approach based on Focused Ion Beam microstructuring to identify crystalline microparticles within a powder sample and to shape them into geometries suitable for resistivity measurements. Our goal is to identify the materials parameters and the intrinsic physics of crystalline materials early on in the research process, before large scale single crystals are available.
As an example, we discuss the role of two-dimensionality in layered iron-arsenide superconductors and the microscopic imprints in their order parameter structure arising from their layered nature. Our conclusions are based on out-of-plane measurements in micron-sized single crystalline structures. We will show transport evidence that an interlayer order parameter modulation in the anisotropic iron-arsenide (V2Sr4O6)Fe2As2 leads to intrinsic Josephson junctions within the crystal unit cell; thereby showing the first example of a multi-band intrinsic Josephson system. The intrinsic junctions are identified by periodic oscillations of the flux flow voltage upon increasing a well aligned in-plane magnetic field, which are observed over an extended temperature range. This periodic flux flow modulation is a hallmark signature of Josephson vortices confined junctions within the unit-cell, and is quantitatively explained by commensurability effects between the Josephson vortex lattice and the crystal structure. These observations suggest the iron-pnictide (V2Sr4O6)Fe2As2 to be an interesting candidate for novel phase-coherent quantum applications exploiting the multi-band nature of the material.
The more isotropic compound SmFeAs(O,F) presents an intriguing example of a weaker inter-layer modulation of the order parameter that is too subtle to form Josephson junctions but strong enough to significantly influence the vortex structure. This impartial suppression leads to a new type of “hybrid vortex” matter, sharing characteristics of both Abrikosov- and Josephson-type vortices. We show the fingerprints of these novel vortices in an unusal field- and temperature dependence of vortex commensurability oscillations and compare the results to numerical Ginzburg-Landau simulations of vortices subjected to a weak special modulation of the order parameter. These results improve our understanding of the pinning potential landscape in these materials and are of relevance for their use in high-Tc applications.
3:00 PM - EP13.1.02
Tuning the Jc Anisotropy in Thick YBCO Films on Technical Templates by Artificial BaHfO3 and Ba2Y(Nb/Ta)O6 Pinning Centers
Patrick Pahlke 1,Max Sieger 1,Jens Haenisch 2,Rainer Nast 2,Bernhard Holzapfel 2,Alexander Usoskin 3,Jan Stroemer 3,Mayraluna Lao 4,Michael Eisterer 4,Alexander Meledin 5,Gustaaf Van Tendeloo 5,Marco Bianchetti 6,Alexander Kursumovic 6,Judith Driscoll 6,Kornelius Nielsch 1,Ludwig Schultz 1,Ruben Huehne 1
1 Institute for Metallic Materials IFW Dresden Dresden Germany,2 Institute for Technical Physics Karlsruhe Institute of Technology (KIT) Karlsruhe Germany3 Bruker HTS GmbH Alzenau Germany4 Atominstitut TU Wien Vienna Austria5 EMAT, Department of Physics University of Antwerp Antwerp Belgium6 Department of Materials Science and Metallurgy University of Cambridge Cambridge United Kingdom
Show AbstractSo far, YBa2Cu3O7-x (YBCO) or related compounds are the most promising materials for the realization of coated conductor applications. Over the last 20 years, significant efforts have been made to develop biaxially textured templates for such conductors for long length manufacture. One major approach for the preparation of cube textured buffer layers on arbitrarily textured metal tapes is the application of ion beam assisted deposition (IBAD) or alternating beam assisted deposition (ABAD). Alternatively, highly textured metal templates are realized by the rolling assisted biaxially textured substrate (RABiTS) approach. More recently, significant efforts are devoted to enhance the current transport capability of the superconducting layers in magnetic fields by nano-engineering the microstructure. Therefore, nanometer-sized artificial pinning centers need to be implemented in the YBCO matrix with an optimized density and distribution.
We deposited YBCO layers with a thickness of 1 µm and above on buffered Ni-W RABiTS substrates as well as on ABAD-YSZ templates using pulsed laser deposition. Additionally, artificial pinning centers such as BaHfO3 and the mixed double-perovskite Ba2Y(Nb/Ta)O6 were incorporated in these YBCO layers. X-ray diffraction confirmed the epitaxial growth of the superconductor on these templates as well as the biaxially oriented incorporation of the second phase additions in the YBCO matrix. Detailed TEM studies revealed the size and distribution of the nanoparticles in dependence of the growth parameters showing a combination of a-b-oriented plates and c-axis aligned nanorods. A critical current density Jc of up to more than 2 MA/cm2 was determined at 77 K in self-field for 1 µm thick films. Transport measurements were performed on the grown films showing a reduced Jc anisotropy in magnetic fields for the doped samples. The influence of the deposition conditions on the distribution of artificial pinning centers and the resulting transport properties will be discussed in detail.
The authors acknowledge financial support from EUROTAPES, a collaborative project funded by the European Union's Seventh Framework Programme (FP7 / 2007 - 2013) under Grant Agreement no. 280432.
3:15 PM - EP13.1.03
Deconvolution of Vortex Pinning and Grain Boundary Blocking Effects in Biaxially Aligned Bi-2212 Round Wires
Yavuz Oz 3,Jianyi Jiang 3,Maxime Matras 3,E. Hellstrom 3,David Larbalestier 3
1 Applied Superconductivity Center Tallahassee United States,2 National High Magnetic Field Laboratory Tallahassee United States,3 Florida State University Tallahassee United States,
Show AbstractThe upper limit to the critical current density Jc is determined first by vortex pinning but Jc is then frequently reduced by defects that limit the connectivity of the sample. For all cuprates, grain boundaries (GBs) tend to obstruct current whenever the grain-to-grain misorientation exceeds ~5°. Round wires of Bi-2212 are a very interesting case because they develop very high Jc when processed under pressure to make full physical connectivity and because recent work by Kametani et al. reveals a strong biaxial texture with a full-width at half-maximum (FWHM) of 15°. Unlike REBCO and Bi-2223 where a critical angle of ~5° is well established, there are no signs of weak link behavior in 2212 wires. However, 2212 can be strongly overdoped (REBCO and 2223 cannot), making the observation of high Jc without weak links with FWHM of 15° plausible. Our work involves varying the doping state of both fully and partially dense Bi-2212 round wires which should affect both the vortex pinning strength and the GB superfluid density. We observed that the change in pinning strength varied much less with doping state as compared to the magnitude of Jc and the magnetization hysteresis, implying that underdoped grain boundaries have a more significant effect on the connectivity of Bi-2212 than previously thought. The significance of finding a cuprate with a significantly larger critical angle than REBCO is immense and the wide doping range of Bi-2212 makes its study very interesting.
3:30 PM - *EP13.1.04
Optimal, Nanodefect Configurations via Strain-Mediated Assembly for Optimized Vortex-Pinning in High-Temperature Superconducting Wires in a Wide Operating Temperature Regime from 4.2K-77K
Amit Goyal 2
1 SUNY - Buffalo Buffalo United States,2 Oak Ridge National Laboratory Oak Ridge United States,
Show AbstractEngineered nanoscale defects within REBa2Cu3O7-δ (REBCO) based coated conductors are of great interest for enhancing vortex-pinning, especially in high-applied magnetic fields. We have conducted extensive research to optimize vortex-pinning and enhance Jc via controlled introduction of various types of nanoscale defects ranging from simple rare-earth oxides and Ba-based perovskites to double perovskite rare-earth tantalates and niobates (Ba2RETaO6 and Ba2RENbO6). This talk will provide an overview on how density, morphology, and composition of these engineered nanoscale defects affects vortex-pinning in different temperature, field and angular regimes. Detailed microstructural and superconducting properties coated conductors with these engineered defects will be presented. It will be shown that certain nanodefect configurations that provide the best performance at high-operating temperatures also provide the optimal properties at low operating temperatures out to high-applied magnetic fields.
4:30 PM - EP13.1.05
Large Pinning Forces and Matching Effects in YBa2Cu3O7-δ Thin Films with Ba2Y(Nb/Ta)O6 Nano-Precipitates
Jens Haenisch 1,Lars Opherden 2,Max Sieger 3,Alexander Meledin 4,Marco Bianchetti 5,Patrick Pahlke 3,Rainer Nast 1,Ludwig Schultz 3,Gustaaf Van Tendeloo 4,Judith Driscoll 5,Ruben Huehne 3,Bernhard Holzapfel 1
1 Karlsruhe Institute of Technology Eggenstein-Leopoldshafen Germany,2 HZDR Dresden Germany3 IFW Dresden Dresden Germany4 University of Antwerp Antwerp Belgium5 University of Cambridge Cambridge United Kingdom
Show AbstractYBa2Cu3O7-δ based coated conductors have large potential in such diverse applications as wires/cables, motors/generators, high-field coils, and superconducting permanent magnets, each of them with a certain range of temperature and magnetic field and a certain need in magnitude and isotropicity in critical current density Jc. In order to use the full potential of YBa2Cu3O7-δ, it is mandatory to tailor its transport properties for the envisaged application. This is done by inserting artificial pinning centers, such as perovskites (e.g. BaZrO3) or (mixed) double-perovskites, which precipitate as nanoparticles and/or nanorods.
We report on a study on the addition of the mixed double perovskite Ba2Y(Nb/Ta)O6 to YBa2Cu3O7-δ thin films on SrTiO3 single crystals prepared by pulsed laser deposition. Size, shape, density and orientation distribution of these pinning centers are analysed by X-ray diffraction and TEM. The electrical transport properties are determined in 4-point geometry in maximum-Lorentz force configuration in fields up to 9 T on bridges prepared by laser cutting.
For small deposition rates, Ba2Y(Nb/Ta)O6 grows as well oriented, densely distributed nanocolumns (D = 10 nm). We achieved a pinning force density of 25 GN/m3 at 77 K at the matching field of 2.3 T, which is among the highest values reported for YBa2Cu3O7-x. The field dependence of the pinning force density and the anisotropy of the critical current density show a complex behavior which is explained by a matching effect of the magnetic field’s c-axis component and the superposition of up to three pinning components. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) elucidates the depinning mechanism, changing from double-kink excitation below the matching field to pinning-potential-determined creep above.
4:45 PM - *EP13.1.06
Doubling In-Field Critical Current in HTS Coated Conductors by a Roll-to-Roll Ion Irradiation Process
Qiang Li 1
1 Brookhaven National Lab Upton United States,
Show AbstractCuprate high temperature superconducting (HTS) cables offer powerful opportunities for increasing capacity, reliability, and efficiency of the electricity grid. HTS coils can provide an alternative to rare-earth permanent magnets used in rotary machines and generators. Increasing their current capacity in the presence of magnetic fields is critical for HTS application in generators for wind turbines, propulsion motors, magnets used in accelerators and medical imaging machines. Here, we present our recent study carried out at BNL’s Tandem Van de Graaff facility. We demonstrated a roll-to-roll irradiation process on production long length coated conductors that resulted in uniform enhancement of critical current in the 4 – 50 K at magnetic field above 1.5T using 18 MeV Au ions at a dose of 6x1011 Au ions/cm2.[1] The moderate ion energies used here are readily accessible with commercial electrostatic generators.
*This work was primarily supported by the US Department of Energy, Advanced Research Project Agency-Energy (ARPA-E), in collaboration with T. Ozaki, C. Zhang, L. Wu, M. W. Rupich, and V. Solovyov. T. Ozaki, C. Zhang, and L. Wu were supported by DOE Office of Science, Materials Sciences and Engineering Division.
[1] Martin Rupich, Q. Li et al, “Engineered Pinning Landscapes for Enhanced 2G Coil Wire” EUCAS 2015.
5:15 PM - EP13.1.07
Two-Step Buffer Aided Top Seeded Infiltration and Growth Process: A New Fabrication Technique for Producing Large, Single Grain (RE)BaCuO Bulk Superconductors
Devendra Namburi 1,Yunhua Shi 1,Kysen Palmer 1,Anthony Dennis 1,John Durrell 1,David Cardwell 1
1 University of Cambridge Cambridge United Kingdom,
Show Abstract(RE)BaCuO bulk high temperature superconductors fabricated in the form of large, single grains can generate magnetic fields that are an order of magnitude higher than those achievable using conventional permanent magnets. The microstructures of these materials are known to play a key role in determining their superconducting properties, such as critical current density and resultant trapped field.
The Seeded Infiltration and Growth (SIG) process is an alternative to conventional Top Seeded Melt Growth (TSMG) for growing (RE)BCO bulk superconductors since it overcomes drawbacks such as porosity, sample shrinkage and inhomogeneity in the distribution of (RE)2BaCuO5 (RE-211) content across the volume of the samples, which are inherent to the TSMG process. However, due to the complexity in the growth process, it is not trivial to make single grain samples more reliably via the SIG process. Furthermore, to date the superconducting properties exhibited by infiltration grown samples are inferior compared to their counter parts made by conventional TSMG.
In the present work, we report a modified TSIG technique referred as Two-step buffer-aided Top Seeded Infiltration and Growth process. This technique has made the growth process more straightforward and very reliable. Additionally, this near-net shaping technique has enabled better control of RE-211 in the fully processed bulk superconductor, which has led to an improvement in flux pinning for practical applications. YBCO samples up to a diameter of 32 mm have been fabricated successfully by this new technique. A typical, 25 mm diameter YBCO sample has exhibited a trapped field of 0.84 T at 77 K. Details of the development of this novel fabrication technique will be presented and the results achieved will be discussed.
5:30 PM - EP13.1.08
Evidence for Strong Variation of Chemical Composition and Superconducting Properties in Low Angle Ca-Doped YbBa2Cu3O7-δ Grain Boundaries
Fumitake Kametani 1,David Larbalestier 1,Dmytro Abraimov 1,P. Li 1,A. Polyanskii 1
1 National High Magnetic Field Laboratory, Applied Superconductivity Center Florida State University Tallahassee United States,
Show AbstractCurrent blockage at grain boundaries (GBs) has been the central problem for high temperature superconductor (HTS), demanding complicated and/or expensive processing for wire fabrications. With the drawback of Tc suppression, it is known that Ca doping can improve critical current density Jc across [001] tilt low angle (5-7°) GBs (LAGBs) in REBa2Cu3O7-δ (RE123). Although previous works suggested possible scenarios, its mechanism has not been fully understood. Here we report atomic-structural and stoichiometry studies of Ca-doped Yb123 [001] tilt LAGBs by using atomic resolution analytical scanning transmission electron microscopy (STEM). By Ca doping, LAGBs can be considered as two distinct regions, the GB dislocations and channels, former of which strengthen superconductivity of the latter by providing excess hole carriers. The strained regions at GB dislocations expand ~3 times by preferential Ca substitution with Yb and Cu, attracting excess oxygen. Meanwhile local Ca content decreases by ~50% at the GB channels. Both of these suppress oxygen δ at the GB channels, producing the similar effect of local oxygen overdoping that provides more hole carriers.
Symposium Organizers
John Durrell, University of Cambridge
Luisa Chiesa, Tufts University
Kazumasa Iida, Nagoya University
Takanobu Kiss, Kyushu University
Marina Putti, Università di Genova
Symposium Support
ESAS European Society for Applied Super Conductivity
JECC TORISHA Co., Ltd.
Research Institute of Superconductor Science and Systems, Kyushu University
EP13.2: Crystals and Devices
Session Chairs
Takanobu Kiss
Paul Seidel
Wednesday AM, March 30, 2016
PCC North, 200 Level, Room 226 B
9:30 AM - *EP13.2.01
Tailoring the Superconducting Properties of AEFe2As2 by the Epitaxial Strain and the Field-Induced Carrier Doping
Takafumi Hatano 1
1 Nagoya University Nagoya City Japan,
Show AbstractTo tailor or design the properties of a superconductor, thin film is a very important form of material. We have been studying the film growth of the layered iron pnictide system AEFe2As2 (AE = alkaline earth, henceforth 122 system) by molecular beam epitaxy (MBE). In this talk, we report our recent achievements on two topics: the first epitaxial film growth of Ca-based 122 (Ca122), and the field-effect control of carrier density of Ba-based 122 (Ba122).
Recently, Ca122 is drawing a considerable interest because of the high Tc in Ln-doped (Ln = lanthanide) single crystals reported by several groups. The reported Tc’s are even higher than 45 K and closing up the record Tc of 56 K by LnFeAs(O,F). Hence, the realization of film growth of this system is highly desirable from the view point of both fundamental physics and applications, yet the attempts had not been successful thus far. In this study, we carefully optimized the growth parameters, especially the flux ratios of the source materials. As a result, we have successfully grown epitaxial thin films of the mother compound on various substrates. As the film grown on (La,Sr)(Ta,Al)O3 (LSAT) substrate had the best quality, we then have grown CaFe2(As1-xPx)2 films with various P contents on LSAT substrates and observed clear superconducting transitions. The phase diagram showed a difference from the report on bulk single crystal, i.e., an expansion of the superconducting phase to higher P-content was observed. Our analyses of the structural data indicate that the difference with bulk samples can be explained by the strain effect caused by the lattice mismatch with the substrate, implying that the properties can be controlled by strain-mediated tuning.
In the iron pnictide system, it is interesting that the superconducting nature is strongly affected by both structural deformation and charge carrier doping. To tailor the properties of the material, it is desirable to control these two variables independently. Aliovalent doping introduces structural change through chemical pressure without changing the carrier density. However, it is not possible to change the carrier density alone by chemical substitution, as it induces always a local structural deformation. In this context, an ion-gated transistor, which can accumulate carriers with a density 100 times larger than conventional transistors, would be a powerful tool to scrutinize the effect of changing the carrier density in the iron pnictides. Because of the chemical stability, Ba122 system is one of the most suitable candidates for this class of experiments. We successfully fabricated ion-gated transistors from P-doped Ba122 films, and performed carrier accumulation experiments both for electron doping and hole doping. The gating experiments resulted in slight decrease of Tc for both directions, indicating a new possibility of tailoring the superconducting properties in the iron pnictide systems.
10:00 AM - EP13.2.02
Physical Properties of Superconducting Boron-Doped Diamonds
Taisuke Kageura 1,Masanobu Shibata 1,Masakuni Hideko 1,Yosuke Sasama 2,Takahide Yamaguchi 2,Yoshihiko Takano 2,Hiroshi Kawarada 1
1 Waseda Univ Tokyo Japan,2 NIMS Ibaraki Japan
Show AbstractDiamonds show superconductivity by doping boron heavily. The critical boron concentration is estimated to be around 3×1020 cm-3[1,2]. The first superconducting boron-doped diamond was fabricated by high pressure and high temperature (HPHT) method in 2004, and since then, many groups have challenged to make superconducting diamonds by using several methods. Our group think that Micro-wave Plasma assisted Chemical Vapor Deposition (MPCVD) is the perfect method for growing high quality heavily boron-doped diamond thin films. Using this method, we have succeeded in making Tc(offset)=10K diamonds, and some showed signs of Tc(onset)=25K [3]. In this study, we report the several properties of superconducting diamonds, especially the effect of lattice distortion and lattice relaxation on superconductivity.
Superconducting diamond thin films were synthesized on HPHT Ib single crystal diamond substrate by MPCVD method. H2+CH4+Tri-Metyl-Boron (TMB) gas mixture was used for growth. The Boron concentration in diamonds was controlled by gas ratio ([TMB]/ [CH4], [CH4]/ [Total gas]), deposition temperature, and pressure. We found lattice orientation dependence of Tc. Tc of (111), (100) and (110) superconducting diamonds rise with increasing boron concentration, then Tc of (100) and (110) diamonds saturate around 4K but only Tc of (111) diamond does not saturate and we achieved Tc(offset)=10K and boron concentration=1×1022 cm-3. We revealed that this difference is caused by lattice distortion. In (100) diamonds, if boron atoms exist at the substitutional site, the lattice always expand in both perpendicular and horizontal directions. On the other hand, in (111) diamonds, two type of lattice expansion is considered. One type is the same as (100) and the other type is only perpendicular expansion. And our superconducting (111) diamonds showed only perpendicular lattice expansion measured by (113) reflection asymmetric Reciprocal Space Mapping (RSM). We also revealed the lattice relaxation and the relationship between critical thickness and boron concentration. Heavily boron doped diamonds with a boron concentration of 1021 cm-3 have lattice constants that are 0.2-0.7% larger than that of pure diamonds. Due to this lattice mismatch, lattice strains appear and once the doped diamond film reaches a certain thickness, relaxation of the lattice strain caused by in-plane stress begins to occur. This thickness is called critical thickness. We observed that the critical thickness becomes thinner with increasing boron concentration, and the thinnest thickness was obtained when the boron concentration is 1×1022 cm-3.
We will report on other physical property on the day of presentation.
[1] YoshihikoTakano, Hiroshi Kawarada et al., APL, 85 2853 (2004)
[2] Akihiro Kawano, Hiroshi Kawarada et al., Phys. Rev. B 82, 085318 (2010)
[3] Hiroyuki Okazaki, Hiroshi Kawarada, Yoshihiko Takano et al., APL, 106, 052601 (2015)
10:15 AM - EP13.2.03
Growth and Study of Superconducting Properties of FeTe0.6Se0.4-xSx (x = 0, 0.05 and 0.10) Single Crystals
Sudesh Sudesh 2,Rohit Kumar 1,Ghanshyam Varma 1
2 School of Physical Sciences J.N.U. New Delhi India,1 I I T Roorkee Roorkee India
Show AbstractFeSe(Te), which belongs to the Fe-based family of superconducting compounds, has the simplest crystal structure. It consists of only the continuous stacking of tetrahedral Fe(Se/Te)4 layers arranged along the c-axis. Fe1+yTe with crystal structure analogous to Fe1+ySe does not show superconductivity but rather undergoes a structural transition from tetragonal to orthorhombic near 70 K. However, chemical doping at the Te-site in Fe1+yTe system with Se or S gives rise to superconductivity. Highest Tc (~ 15 K) is observed when Se substitutes for Te in FeTe system with the composition FeTe1-xSex (x = 0.50). As this compound has an extremely simple crystal structure, excellent response to external pressure and the less toxic Se in comparison to As in pnictides, it presents a better model to study the interplay between structure, superconductivity and magnetism in the Fe-based superconducting compounds. In order to study the effect of varying the lattice parameters of FeTe0.6Se0.4 system on its superconductivity and magnetism, we have used S to substitute at the Se-site. We have grown single crystalline samples of FeTe0.6Se0.4-xSx (x = 0, 0.05 and 0.10) using self-flux technique and studied the structural, electrical transport and magnetic properties of the as-grown crystals. The single crystals obtained are plate like and appear black with shining texture. The X-ray diffraction done on the cleaved surface confirms that the plane of cleaved surface is (0 0 l). The powder X-ray diffraction done on the powdered single crystals reveals a single (tetragonal) phase with space group symmetry P4/nmm for all the samples. We have observed that the lattice parameters a and c decrease slightly with S-substitution at the Se-site in FeTe0.6Se0.4 due to smaller ionic radius of S as compared to Se. This is also clear from the shifting of (0 0 l) peaks to higher angles. The temperature dependence of resistivity measurements is done for all the samples. It is observed that the value of Tc (~ 14 K for x = 0) decreased with the substitution of S (~ 9 K for x = 0.10), which is also confirmed from ac-susceptibility measurements. The resistivity measurements for all the samples have also been done in the presence of magnetic fields (0 – 8 T) to estimate the upper critical field (Hc2) and irreversibility field (Hirr) values using the criteria of Hc2 = H(0.9ρn) and Hirr = H(0.1ρn). The values of Hc2(0) have been calculated by fitting the experimental data with GL-theory: Hc2(T) = Hc2(0)(1-t2)/1+t2), where t = T/Tc. The value of Hc2(0) ( ~170 T) observed is highest for x = 0. The high sensitivity of superconductivity towards structure has been observed in the present study.
10:30 AM - *EP13.2.04
Spectromicroscopy of Phase-Separated Iron-Based Superconductors
Susannah Speller 1,Tayebeh Mousavi 1,Pavel Dudin 2,Chris Grovenor 1
1 Univ of Oxford Oxford United Kingdom,2 Diamond Light Source Didcot United Kingdom
Show AbstractUnderstanding the interplay between superconductivity and magnetism in iron-based superconductors is likely to provide significant insights into the elusive mechanisms responsible for high temperature superconductivity. The co-existence of magnetic order and superconductivity is a common feature of the iron-based superconductors, raising the question of whether these phases are spatially distinct or whether the same electrons are responsible for both phenomena.
In the case of the AxFe2−ySe2 compounds, with Tc values of about 30K, the intrinsic phase separation is very extreme, with significant chemical and structural differences associated with the spatially distinct electronic phases. Here we will present recent results on the microstructural development of AxFe2−ySe2 single crystals upon annealing, and how this influences their superconducting/magnetic properties. In addition to analytic electron microscopy studies, scanning photoemission microscopy (SPEM) has been used to investigate the differences electronic structure between the two phases, enabling direct correlation between the electronic properties and chemistry/structure of each phase. Recent work using Photoemission electron microscopy (PEEM) to carry out spatially resolved core level X-ray Absorption Spectroscopy and linear dichroism experiments will also be reported.
11:30 AM - EP13.2.05
Trapped Magnetic-Field Properties of Dense MgB2 Bulks Synthesized by Infiltration-Capsule Method
Tomoyuki Naito 1,Arata Ogino 1,Hiroyuki Fujishiro 1
1 Iwate University Morioka Japan,
Show AbstractMgB2 superconducting bulk magnets have been intensively studied for the past five years. Since it is well known that the grain boundaries are predominant pinning centers for MgB2, the refinement of grains and/or the densification have improved the trapped field properties. Recently, a hot pressed (HPed) MgB2 bulk using the ball-milled nano-powder trapped 5.4 T at 12 K [1]. We also obtained the trapped field of 4.6 T at 14 K at the center of doubly stacked Ti-doped bulks fabricated by a hot isostatic pressing (HIPing) method [2]. The dense MgB2 bulks can also be synthesized by an infiltration method without pressing and specific furnace, contrary to the HP and HIP methods. Giunchi et al. succeeded in fabricating large and dense MgB2 bulk by a reactive liquid Mg infiltration (Mg-RLI) method [3], and trapped field of 2 T at 20 K was obtained for the bulk with 55 mm in diameter. In this paper, we prepared MgB2 bulks (about 30 mm in diameter) by the infiltration method in a home-made closed capsule and evaluated their trapped field and vortex pinning properties. The filling factor of the obtained bulk was estimated to be about 90% and the critical temperature defined at the mid-point of the magnetic transition was about 38 K. The bulk was magnetized by a field cooled magnetization under a magnetic field of 5 T. The trapped field at the center of the bulk surface was 2.4 T at 16.2 K, which was comparable with that of the HIPed bulk with the similar density and size. We discuss a potential of the MgB2 bulk fabricated by the infiltration method as the superconducting bulk magnet.
References
[1] G. Fuchs et al., Supercond. Sci. Technol. 26 (2013) 122002.
[2] T. Naito et al., Supercond. Sci. Technol. 28 (2015) 095009.
[3] G. Giunchi et al., Int. J. Mod. Phys. B 17 (2003) 453.
Acknowledgements:
This work was partly supported by JSPS KAKENHI Grant Numbers 15K04718, 15K04646.
11:45 AM - *EP13.2.06
Josephson Junctions with Iron-Based Superconductors
Paul Seidel 1
1 Friedrich-Schiller University Jena Jena Germany,
Show AbstractA review about progress in fabrication, measurements and theoretical interpretation of Josephson effects in the new iron-based superconductors is given. The main properties and parameters of Josephson junctions with respect to basic understanding as well as to future applications like the product of critical Josephson current and normal resistance are discussed. Preparation and properties of different types of junctions (artificial barrier SNS, SINS or SIS junctions and bicrystal grain boundary junctions) using thin films or single crystals of iron-based superconductors as one or both electrodes are compared. Temperature and magnetic field dependencies as well as the effects of microwave irradiation are measured and compared to theoretical models. New designs will be introduced to realize phase sensitive junctions for investigation of the pairing symmetry in the iron-based superconductors.
12:15 PM - EP13.2.07
Bias Sputtered Few-Nanometer-Thick Niobium Nitride for Superconducting Devices
Andrew Dane 1,Karl Berggren 1
1 Massachusetts Institute of Technology Cambridge United States,
Show AbstractFew-nanometer-thick films of low temperature superconducting materials have become increasingly important for sensitive photonic devices. Hot electron bolometers (HEB), superconducting nanowire single photon detectors (SNSPD), microwave kinetic inductance detectors (MKID) and transition edge sensors (TES) are all broadband, highly sensitive photo-detectors that are fabricated from thin films of low temperature superconducting materials.
Improvements to materials synthesis and exploration of materials dependent properties of these devices has so far taken a back seat to advancing the performance of individual devices through electrical design. In particular, while the performance of individual few-nanometer-thick niobium nitride (NbN) SNSPDs has produced detectors with near unity quantum efficiency and tens of picoseconds of jitter, yield of these devices remains a major issue. As optical systems demand longer nanowire devices and arrays of devices, previously ignored yield issues must be addressed. Promising results have been achieved in superconducting amorphous tungsten silicide (WSi), suggesting that yield is improved by moving from a polycrystalline material system such as NbN to an amorphous one. However, the operating temperature required for efficient operation of WSi SNSPDs (
In this work we explored reactive DC magnetron sputtering of few-nanometer-thick NbN without intentional substrate heating, as well as the performance of superconducting devices made from this material. We have found that for films with thicknesses typical of those used to fabricate SNSPDs, the addition of a large substrate bias and the ion bombardment that results during film deposition significantly reduces the film resistivity, increases the Tc and decreases the film roughness. The film surface morphology is changed significantly. This material shows promise for fabricating SNSPDs with improved yield, increased efficiency and at easy to access temperatures. Additionally, a host of fabrication methods and structures become practical when heating of the substrate is not required.
12:30 PM - EP13.2.08
Superconductors for Single Photon Detectors: Crystalline or Amorphous
David Bosworth 1,Robert Hadfield 2,Zoe Barber 1
1 Department of Materials Science amp; Metallurgy University of Cambridge Cambridge United Kingdom,2 School of Engineering University of Glasgow Glasgow United Kingdom
Show AbstractSuperconducting nanowire single photon detectors (SNSPDs) have attracted much interest due to their the higher detection efficiencies, lower jitter counts and, most importantly, faster reset times allowing for operation at telecoms wavelengths. The first devices were fabricated using highly crystalline NbN as the superconductor [1]. NbN and NbTiN continue to dominate the field in terms of wide use however a new generation of devices based on amorphous superconductors such as WSi or MoSi are beginning to challenge for the highest detection efficiencies at a wide range of wavelengths [2]; their reduced superconducting energy gap results in larger hotspot formation allowing for detection of lower energy photons. The amorphous nature allows for a more homogenous film to be grown which results in a spatially uniform detection efficiency and higher internal quantum efficiency.
The conflicting growth requirements of crystalline and amorphous films provide an interesting study in to the material science required for the different growth mechanisms. Additionally, other device requirements, such as thermally unstable ion implanted waveguides or reflective layers below the detector, place restrictions on the growth parameters meaning non-deal conditions must be optimised.
In this work we present the state of the art for different approaches to SNSPD fabrication within the context of the materials used. Our work in optimising both crystalline NbN and amorphous MoSi [3] films provides an important backdrop to the observations of other research groups. With different advantages and disadvantages, a better understanding of the materials themselves is vital for continued development of SNSPDs.
[1] A.D. Semenov et al Quantum detection by current carrying superconducting film Phys. C Supercond. Its Appl. 351, 349, 2001
[2] B Baek et al Superconducting a-WxSi1−x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm APL, 98 25, 251105, 2011
[3] D. Bosworth et al, Amorphous molybdenum silicon superconducting thin films, AIP Adv. 5, 087106, 2015
EP13.3: Wires and Tapes
Session Chairs
Wednesday PM, March 30, 2016
PCC North, 200 Level, Room 226 B
2:45 PM - *EP13.3.01
REBCO Coated Conductors with Excellent Performance in High Magnetic Fields
Venkat Selvamanickam 1,Meysam Heydari Gharahcheshmeh 1,Rudra Pratap 1,Aixia Xu 1,Yuan Zhang 1,Eduard Galstyan 1,Ann Soriaga 1,Goran Majkic 1
1 University of Houston Houston United States,
Show AbstractIn the past few years, tremendous advancements have occurred in nanoscale defect engineering in REBCO coated conductors that has led to a quadrupling of critical current performance in high magnetic fields and operating temperatures of interest for various applications. REBCO tapes have been fabricated with a high density of nanoscale defects with zirconium addition up to 25 mol% with excellent properties in magnetic fields of 2 – 30 T over a temperature range of 4.2 K to 77 K. Critical current densities exceeding 20 MA/cm2 have been achieved at 30 K, 3 T (field perpendicular to tape) and pinning forces over 1000 GN/m3 have been attained at 20 K. Combining these heavily-doped REBCO with thicker films, engineering current densities above 2200 A/mm2 have been demonstrated at 4.2 K in 15 T field oriented perpendicular to the tape plane, which is twice and thrice respectively better than the performance levels of Nb3Sn and Bi-2212 wires at this field. An overview of the development of high performance REBCO coated conductors for high field applications will be presented.
This work was supported the Advanced Research Projects Agency-Energy, Office of Naval Research and Argonne National Laboratory.
3:15 PM - *EP13.3.02
Development of Application-Oriented DI-BSCCO Wires
Takayoshi Nakashima 1,Shinichi Kobayashi 1,Goro Osabe 1,Tomohiro Kagiyama 1,Kouhei Yamazaki 1,Masashi Kikuchi 1,Souichirou Takeda 1,Takurou Kadoya 1,Tomoyuki Okada 1
1 Sumitomo Electric Industries Osaka Japan,
Show AbstractSumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires, DI-BSCCO (Dynamically-Innovative BSCCO). The wires have been improved various properties in response to the growing demands from the application products and projects.
DI-BSCCO wires are laminated with high-strength materials for high-field applications to endure the intense hoop stress. Such applications also need higher critical current density, especially, engineering critical current density (Je) to make the magnets lighter and more compact. Although the thinner reinforcement materials are inevitable for high Je, the thickness and strength are incompatible with each other. This fact urged us to explore the new potential materials for reinforcement with higher strength beyond stainless steel. Among the reviewed materials, Ni-Cr alloys have been focused on as the promising reinforcement materials.
The reinforcement with the thin (30 μm-thick) Ni-Cr alloys has considerably enhanced the mechanical properties of DI-BSCCO wires. For example, critical double bending diameter at room temperature ~ 34 mm, critical tensile stress at 77 K ~ 435 MPa, and critical tensile strain at 77 K ~ 0.5 %. The wires laminated with Ni-Cr alloys were previously called Type HT-XX (~2014) and have been officially named Type HT-NX (2015~). In this talk, the detailed performances of the currently available wires and the updated R&D activities will be shown.
EP13.4: Modeling
Session Chairs
Wednesday PM, March 30, 2016
PCC North, 200 Level, Room 226 B
4:15 PM - *EP13.4.01
Quasiparticle Interference in Strongly Coupled Multiband Superconductors
Alexander Golubov 2
1 University of Twente Enschede Netherlands,2 Moscow Institute of Physics and Technology Moscow Russian Federation,
Show AbstractThe field of superconductivity in Fe-based compounds is abuzz with the search for a technique to unambiguously determine the gap symmetry and its structure. There have been many proposals in the past have been made with regard to the above and a lot of experiments done employing various techniques. Nonetheless, the quest for the irrefutable underlying superconducting mechanism seems to have hopes pinned on the quasiparticle interference (QPI) data interpretation , in a qualitative manner, from the Fourier transformed STM measurements. In this work, we show that the idea of using QPI is a probe for the gap symmetry needs to be addressed thoroughly, such
that the various aspects of the phenomena are explored from the weak coupling to the strong coupling regime. Here, we utilize the well known strong interaction Eliashberg theory as a calculation tool to probe the two regions and extract the physical meanings of the QPI for s++ and s�+- , intraband and interband transitions respectively, at both the scales in a quantitative manner. Although, the
full knowledge of the gap symmetry itself wont divulge any associated structural details of the order parameter and the mass gap, yet it has a strong bearing upon the pairing mechanism or the proverbial "bosonic gule" of high temperature superconductivity.The method of using the quasiparticle interference for classifying symmetry of the superconducting gap seems very promising and needs to be addressed extensively in order to significantly enhance the knowledge of superconducting mechanism in pnictides.
4:45 PM - EP13.4.02
Superconductivity Near the Metal-Insulator Transition
Michael Osofsky 1,Joseph Prestigiacomo 1,Clifford Krowne 1,Robert Soulen 2,Eleanor Clements 3,Gerald Woods 3,Hari Srikanth 3,Ichiro Takeuchi 4
1 Naval Research Lab Washington United States,1 Naval Research Lab Washington United States,2 Retired Washington United States1 Naval Research Lab Washington United States,3 University of South Florida Tampa United States3 University of South Florida Tampa United States4 University of Maryland College Park United States
Show AbstractFor conventional superconductors, the superconductive critical temperature can be characterized by the coupling strength, λ=NV where N is the single particle density of states and V is an attractive potential. The search for new superconductors with high Tc often involves searching for materials with enhanced N. In this presentation we explore an alternative approach that entails enhancing V. We demonstrate empirically that several disparate classes of superconductors share a common phase diagram Tc(r) where r is a coordinate characterizing the distance to the MIT. This phase diagram may be explained by explicitly incorporating the novel properties of the MIT in V. We discuss the implications of this model on HTS and how this framework can be used as a guide in the search for new superconductors.
5:00 PM - EP13.4.03
Application of Metamaterial Nanoengineering for Increase of Superconducting Critical Temperature
Vera Smolyaninova 1,Kathryn Zander 1,Thomas Gresock 1,Christopher Jensen 1,Joseph Prestigiacomo 2,Michael Osofsky 2,Igor Smolyaninov 3
1 Towson Univ Towson United States,2 Naval Research laboratory Washington United States3 University of Maryland College Park United States
Show AbstractWe have demonstrated that metamaterial approach to dielectric response engineering, increases the critical temperature of a composite superconductor-dielectric metamaterial in epsilon near zero (ENZ) regime. To create such metamaterial superconductors two approaches were implemented. In the first approach, mixtures of tin and barium titanate nanoparticles of varying composition were used [1]. An increase of the critical temperature of the order of 5% compared to bulk tin has been observed for 40% volume fraction of barium titanate nanoparticles. Similar results were also obtained with compressed mixtures of tin and strontium titanate nanoparticles. In the second approach, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium [2]. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the ENZ metamaterial approach to Tc engineering. The developed technology enables efficient nanofabrication of bulk aluminium-based metamaterial superconductors. These results open up numerous new possibilities of considerable Tc increase in other superconductors. This work was supported in part by NSF grant DMR-1104676.
References
1. Vera N. Smolyaninova, Bradley Yost, Kathryn Zander, M. S. Osofsky, Heungsoo Kim, Shanta Saha, R. L. Greene, and Igor I. Smolyaninov, Scientific Reports 4, 7321 (2014).
2. Vera N. Smolyaninova, Kathryn Zander, Thomas Gresock, Christopher Jensen, Joseph C. Prestigiacomo, M. S. Osofsky, and Igor I. Smolyaninov, (2015), in press.
5:15 PM - *EP13.4.04
Modelling of Bulk Superconductor Magnetization
Mark Ainslie 1,Hiroyuki Fujishiro 2,Jin Zou 1
1 University of Cambridge Cambridge United Kingdom,2 Department of Materials Science and Engineering Iwate University Morioka Japan
Show AbstractIn this presentation, the authors present a summary of some of the current state-of-the-art in modelling the magnetization of bulk superconductors, including both (RE)BCO (where RE = rare earth or Y) and MgB2 materials. Such numerical modelling is a powerful tool to understand the physical mechanisms of bulk superconductor magnetization, to assist in interpretation of experimental results, and to predict the performance of practical bulk superconductor-based devices, which is particularly important as many superconducting applications head towards the commercialisation stage of their development in the coming years. The presentation highlights the differences between simulating the different magnetizing techniques – zero field cooling (ZFC), field cooling (FC) and pulsed field magnetization (PFM) – as well as the differences and similarities of the assumptions made for the numerical simulation related to bulk (RE)BCO and MgB2 samples.
5:45 PM - EP13.4.05
Nanocomposite YBa2Cu3O7-δ Thin Films Using Chemical Solution Deposition and Preformed Nanocrystals
Glenn Pollefeyt 1,Hannes Rijckaert 1,Katrien De Keukeleere 1,Pablo Cayado 2,Alexander Meledin 3,Jonathan De Roo 1,Max Sieger 4,Ferran Valles 2,Mariona Coll 2,Anna Palau 2,Ruben Huehne 4,Ron Feenstra 5,Jan Bennewitz 5,Gustaaf Van Tendeloo 3,Xavier Obradors 2,Teresa Puig 2,Michael Baecker 5,Maximilian Hemgesberg 6,Isabel Van Driessche 1,Klaartje DeBuysser 1
1 Ghent University Ghent Belgium,2 ICMAB-CSIC Bellaterra Spain3 University of Antwerp Antwerpen Belgium4 IFW Dresden Dresden Germany5 Deutsche Nanoschicht GmbH Rheinbach Germany6 BASF Ludwigshafen am Rhein Germany
Show AbstractThe implementation of YBa2Cu3O7-δ coated conductors in large scale applications generally requires an improvement of the superconductors’ in-field performance. The incorporation of nanostructured secondary phases has proven to be an adequate approach to achieve flux pinning, hereby preventing the drastic decrease of the critical current density Jc at moderate-to-high magnetic fields as well as its angular dependency on the magnetic field. The most effective pinning occurs when the nanometer-sized defects are homogeneously distributed throughout the superconductor. To achieve this, we have produced nanocomposite thin films starting from preformed nanocrystals (PNC) in combination with fluorine-based chemical solution deposition. The use of PNC’s generally offers a better control of the final microstructural properties of the nanocomposite films when compared to self-assembled nanocrystal formation during YBCO processing.
In this work, small ZrO2 and HfO2 nanocrystals were synthesized with diameters in the range of 4 - 8 nm and a narrow size distribution. The NCs are initially capped with hydrophobic ligands, ensuring colloidal stability in apolar solvents. However, as the YBCO precursor typically provides a more polar environment, e.g., methanol, an important aspect of this research involves ligand exchange and the appropriate stabilization procedure. We are able to stabilize these nanocrystals in different types of fluorine-based YBCO precursor solutions, leading to highly stable nanocomposite precursors with long shelf-lives. Afterwards, the YBCO-PNC solutions were deposited on single crystal LaAlO3 substrates via both spin-coating and ink-jet printing. The main focus of this research pointed to understanding the factors which control the microstructure development and the physical properties of the nanocomposite thin films. By strict optimization on both the precursor and processing level, we achieved nanocomposite thin films exhibiting Jc of 4-5 MA/cm2 at 77 K in self-field as well as a much smoother decay of Jc as a function of magnetic field. This is reflected by a strong pinning force enhancement (up to 10 GN/m3 at 77K) and a reduced effective anisotropy (γeff ~ 3) compared to undoped YBCO films.
This newly developed approach delivers scalable and high quality superconducting films, capable of meeting the strict requirements for the successful implementation and distribution of coated conductors throughout energy market.
Symposium Organizers
John Durrell, University of Cambridge
Luisa Chiesa, Tufts University
Kazumasa Iida, Nagoya University
Takanobu Kiss, Kyushu University
Marina Putti, Università di Genova
Symposium Support
ESAS European Society for Applied Super Conductivity
JECC TORISHA Co., Ltd.
Research Institute of Superconductor Science and Systems, Kyushu University
EP13.5: Tailoring Materials II
Session Chairs
Qiang Li
Susannah Speller
Thursday AM, March 31, 2016
PCC North, 200 Level, Room 226 B
10:00 AM - *EP13.5.01
Vortex Pinning in the Fe-Based 122 and 1111 Phases
Chiara Tarantini 1
1 Applied Superconductivity Center, National High Magnetic Field Laboratory Florida State University Tallahassee United States,
Show AbstractThe recently discovered Fe-based superconductors (FBS) include many compounds with different intrinsic and extrinsic properties. In order to understand which of these compounds has potential for applications, many aspects have to be investigated. Here we will focus on the vortex pinning properties in the LnFeAs(O,F) (1111) and AEFe2As2 (122) phases. It has been demonstrated that Co-doped Ba122 with a Tc of only 22 K has an exceptional acceptance of high densities of secondary phases and defects [1,2,3] capable of acting as effective pinning centers with pinning force density up to 84 GN/m3 at 22.5T and 4.2 K [3]. This is the highest value ever reported in any 122 phase and it shows that the in-field performance of Ba122 widely exceeds that of Nb3Sn, potentially making 122 of interest for applications. The 1111 phases are in principle of even greater potential because of their twice higher Tc. We discovered that single layer thin films are influenced by both intrinsic [4,5] and extrinsic pinning [5]. In Nd1111 we found two distinct and weakly interactive extrinsic pinning mechanisms whose contribution independently changes with temperature. Moreover the 1111 phase, because of the larger Tc and larger anisotropy with respect to the 122 phase, behaves as quasi two-dimensional (2D) system with intrinsic vortex pinning properties closer to the high-Tc YBCO than to the low-Tc superconductors.
Work made in collaborations between ASC-National High Magnetic Field Laboratory-Florida State University, Nagoya University, Institute for Metallic Materials – IFW, Karlsruhe Institute of Technology-Institute for Technical Physics, and University of Wisconsin-Madison.
1 C. Tarantini et al., Appl.Phys.Lett. 96, 142510 (2010)
2 C. Tarantini et al., Phys.Rev.B 86, 214504 (2012)
3 C. Tarantini et al., Sci.Rep. 4, 7305 (2014)
4 K. Iida, C. Tarantini et al., Sci.Rep. 3, 2139 (2013)
5 C. Tarantini, K. Iida, F. Kurth, J. Jaroszynski, V. Grinenko, J. Hänisch, B. Holzapfel, S. Schmidt, P.Seidel, N. Sumiya, M. Chihara, H. Ikuta, D.C. Larbalestier, in preparation.
10:30 AM - EP13.5.02
Highly Textured Oxypnictide Superconducting Thin Films on Metal Substrates
Kazumasa Iida 2,Fritz Kurth 3,Masashi Chihara 1,Naoki Sumiya 1,Vadim Grinenko 2,Ataru Ichinose 4,Ichiro Tsukada 4,Jens Haenisch 5,Vladimir Matias 6,Takafumi Hatano 1,Bernhard Holzapfel 5,Hiroshi Ikuta 1
1 Nagoya University Nagoya Japan,2 IFW Dresden Dresden Germany,2 IFW Dresden Dresden Germany,3 TU Dresden Dresden Germany1 Nagoya University Nagoya Japan2 IFW Dresden Dresden Germany4 Central Research Institute of Electric Power Industry Yokosuka Japan5 Karlsruhe Institute of Technology Eggenstein-Leopoldshafen Germany6 iBeam Materials, Inc. Santa Fe United States
Show AbstractElectron or hole doped AEFe2As2 (AE=Ba and Sr) and Fe(Se,Te) show high upper critical fields with low anisotropies at low temperatures that offer a unique possibility for high field magnet applications. The recent progress of powder-in-tube (PIT) technique is remarkable, resulting in high performance AEFe2As2 tapes. Furthermore, Co-doped BaFe2As2 and Fe(Se,Te) on ion beam assisted deposition (IBAD)-MgO/Y2O3/Hastelloy with comparable Jc to those on single crystalline substrates have been demonstrated, although the texture quality of the formers is inferior to the latters [1-3]. On the other hand, LnFeAs(O,F) (Ln=Sm, Nd) is expected to have potentially higher Jc than other Fe-based superconductors (FBS) due to the highest Tc around 55 K among the FBS. However, the level of Jc in PIT-processed SmFeAs(O,F) wire is around 4.0x103 A/cm2 even in low fields at 4.2 K [4], much lower than AEFe2As2 wires. A fundamental reason for the low Jc in oxypnictide may be due to higher sensitivity against the grain misorientation than other FBS, since LnFeAs(O,F) (Ln=Sm, Nd) has more anisotropic crystal structure and superconducting properties, which resembles high-Tc cuprates. Here we report on a preparation of NdFeAs(O,F) thin films on MgO-templated Hastelloy by means of molecular beam epitaxy. The oxypnictide coated conductors showed a Tc of 43 K with a self-field Jc of 7.0x104 A/cm2 at 5 K, more than 20 times higher than powder-in-tube processed SmFeAs(O,F) wires.
1. T. Katase et al. Appl. Phys. Lett. 98, 242510 (2011).
2. W. Si et al. Nat. Commun. 4, 1347 (2013).
3. S. Trommler et al. Supercond. Sci. Technol. 25, 084019 (2012).
4. M. Fujioka et al. Appl. Phys. Express 4, 063102 (2011).
10:45 AM - EP13.5.03
NbN and Nb1-xTixN Thin Films Growth by HTCVD: Structural and Superconducting Properties
Nikolaos Tsavdaris 2,Dibyendu Harza 4,Roman Reboud 1,Salha Jebari 4,Max Hofheinz 4,Elisabeth Blanquet 2,Frederic Mercier 2
1 SIMAP Univ. Grenoble Alpes Grenoble France,2 CNRS,SiMaP Grenoble France,3 INAC/SPSMS CEA-Grenoble Grenoble France,4 Univ. Grenoble Alpes Grenoble France1 SIMAP Univ. Grenoble Alpes Grenoble France
Show AbstractAmong transition metal nitrides, niobium nitride (NbN) stands out as a candidate for single-photon detectors (SSPDs) and superconductive radio frequency (SRF) cavities, due to its excellent superconducting properties. Despite the large number of reports on the electrical features of NbN thin films, only a few studies describe and link the structural characteristics with the superconducting properties. Typically cubic NbN (c-NbN) is deposited using dc magnetron sputtering where growth parameters, substrate or addition of a metallic element are chosen to stabilize the (Fm-3m) cubic phase, which has the highest superconducting critical temperature. Here, we report on the role of Ti in the stabilization and superconducting properties of cubic Nb1-xTixN thin films, grown for the first time (to the best of our knowledge) by high temperature chemical vapour deposition (HTCVD) technique.
NbN and Nb1-xTixN thin films are grown using a HTCVD reactor on different substrates – (0001) oriented single crystal Al2O3, (0001) AlN/Al2O3, and (0001) GaN/Al2O3. The chlorination of the Nb (99,99%) and Ti (99,99%) metallic source occurs in-situ, in a Cl2 (99,999%) chlorination chamber. The reaction by-products with NH3 as well as the deposition procedure are described elsewhere [1]. To access the large parameter range, the thickness of the films is varied from 90 nm down to less than 10 nm, whereas, the deposition temperature is varied from 900oC to 1300oC. To explore the crystal structure and surface morphology, films are characterized by means of SEM (scanning electron microscopy), XRD (X-ray diffraction) and AFM (atomic force microscope). Electrical transport measurements down to 4 K are performed in a commercial Physical Property Measurement System (PPMS).
On the structural side, it was found that for Tdeposition
11:30 AM - *EP13.5.04
Effects of High-Energy Heavy-Ion Irradiations on the Superconducting Properties of Co- and K-doped Ba-122 Single Crystals
Laura Gozzelino 2,Roberto Gerbaldo 2,Gianluca Ghigo 2,Francesco Laviano 2,Tsuyoshi Tamegai 3
1 Department of Applied Science and Technology Politecnico di Torino Torino Italy,2 INFN - Sezione di Torino Torino Italy,3 Department of Applied Physics The University of Tokyo Hongo, Bunkyo-ku, Tokyo Japan
Show AbstractIrradiation is a powerful tool for introducing controlled disorder in superconductors, with the aim both to enhance their performances and to investigate their fundamental physics. For this purpose, particle irradiations have been used to tailor the electromagnetic properties of medium-high temperature superconductors, such as cuprates [1], MgB2 [2] and, at last, iron-based superconductors [3].
In this framework we investigated the effect of 250 MeV and 2 GeV Au-ion irradiations on single crystals of Co-doped Ba-122 (nominal Co doping: 7%) and K-doped Ba-122 (nominal K doping 40%) at a wide fluence range. Firstly, we focused on the analysis of the local current density attained by quantitative magneto-optical imaging, without any model assumption [4]. The critical current density enhancement induced by irradiation as well as its dependence on the magnetic field direction was studied on a micron scale. This allowed us to examine the competition between the anisotropic pinning due to intrinsic planar defects parallel to the ab plane of the crystals and that one due to extrinsic defects, which show a correlation along the ion tracks (c-axis).
We also investigated the high-frequency behavior of the crystals by means of a microwave coplanar resonator technique [5], obtaining the temperature dependence of the superfluid density and of the quasiparticle conductivity. The analysis of samples irradiated to high fluences allows us to discuss the consistency of the data with the leading candidates for the pairing symmetry order parameter, i.e. the multi-gap s++ and s± wave models [6,7], mainly through the dependence of the Tc suppression on disorder.
[1] W. Lang, J. D. Pedarnig, in “Nanoscience and Engineering in Superconductivity”, Springer Berlin Heidelberg Publisher, 2010, p. 81.
[2] X. X. Xi, Rep. Prog. Phys., 71 (2008) 116501.
[3] T. Tamegai et al., Supercond. Sci. Technol., 25 (2012) 084008.
[4] F. Laviano et al., Supercond. Sci. Technol., 27 (2014) 044014 and reference therein.
[5] G. Ghigo et al., submitted.
[6] I. I. Mazin, Nature 464 (2010) 183.
[7] S. Onari and H. Kontani, Phys. Rev. Lett. 103 (2009) 177001.
12:00 PM - EP13.5.05
Clean Superconductivity in Electron Doped Pr2−xCexCuO4: Transport Study
Ai Ikeda 1,Yoshiharu Krockenberger 1,Masafumi Horio 2,Hiroshi Irie 1,Hideki Yamamoto 1
1 NTT Basic Research Laboratories Kanagawa Japan,1 NTT Basic Research Laboratories Kanagawa Japan,2 The University of Tokyo Tokyo Japan
Show AbstractSuperconductivity in RE2−xCexCuO4 competes with antiferromagnetic order due to the occupation of oxygen ions at apical sites. Consequently, these oxygen ions also tune electronic conduction in RE2−xCexCuO4. Here, we show that the upper critical magnetic field (Hc2) of RE2−xCexCuO4 with RE = Pr strongly depends on the residual resistivity ratio (RRR). Single phase, high quality Pr1.85Ce0.15CuO4 (PCCO) thin films (100 nm thickness) were grown by molecular beam epitaxy on SrTiO3 (STO) substrates followed by an in situ vacuum annealing process for the evacuation of apical sites. As the epitaxial relation between PCCO films and STO substrates is relaxed, strain induced modifications of electronic states can be ruled out and the observed superconductivity can be considered as bulk representative [1]. Subject to annealing conditions, PCCO films may be either insulating or metallic (RRR > 1). Superconductivity in PCCO films is formed for RRR > 2. For PCCO films with 2 ≤ RRR ≤ 6 , Hc2 exceeds 7 T whereas RRR > 6, Hc2 may be as small as 2.0 T. This leads to coherence lengths (ξ) 6.8 nm
12:15 PM - EP13.5.07
High-Temperature Superconducting REBCO Conductors for Undulators in X-Ray Sources
Ibrahim Kesgin 1,Charles Doose 1,Matt Kasa 1,Yury Ivanyushenkov 1,Ulrich Welp 1
1 Argonne National Laboratory Lemont United States,
Show AbstractUndulators are the heart of storage ring and free electron laser based light sources that actually generate the hard x-ray radiation. Achieving highly-brilliant, powerful x-ray radiation requires the generation of alternating magnetic field with high magnitude in the undulator. Superconducting undulators (SCUs), primarily wound with NbTi-wire, have been fabricated and shown to be a practical way of increasing the magnetic field from these devices. However, NbTi has nearly reached the limits of its performance. REBCO (RE = rare earth, barium copper oxide) second generation (2G) high temperature superconducting (HTS) coated conductors (CCs) are considered to be a promising alternative to NbTi-wire due to their high engineering current densities and larger temperature stability margin. In this presentation, viability and challenges of using coated conductors as an alternative for undulator windings to further increase the brilliance of x-ray sources will be discussed and our preliminary results will also be presented.
12:30 PM - EP13.5.08
Novel Superconducting Joints for Persistent Mode Magnet Applications
Susannah Speller 1,Tayebeh Mousavi 1,Canan Aksoy 1,Greg Brittles 1,Chris Grovenor 1
1 Univ of Oxford Oxford United Kingdom,
Show AbstractPersistent current joints are a critical component of commercial superconducting magnets.The standard jointing method widely used in the magnet industry for technological low temperature superconducting wires such as NbTi and Nb3Sn wires uses a superconducting solder (e.g. PbBi). In these joints the physical and superconducting properties of the solder materials inevitably play an important role in the overall performance of the joint. Key requirements for superconducting solders include low melting point to prevent degradation of the superconducting filaments during joining, good wettability of the superconducting filaments, suitable liquid phase viscosity, and finally adequate superconducting properties to enable sufficient supercurrent to pass through the joint under typical operating conditions (typically at 4.2K in a field of 1 T for an MRI magnet). PbBi solder satisfies all these criteria, but restrictions on the use of lead in the magnet industry are expected in the relatively near future, so new lead-free jointing techniques need to be developed.
One approach is the development of superconducting lead-free solder materials. In our work, we have focussed on the In-Sn system and ternary systems involving In and Sn as two of the elements. Thermodynamic modelling has been used to produce ternary phase diagrams of potential alloy systems, and various formulations have been fabricated in order to explore how microstructure and phase chemistry influence the superconducting properties of the solders.
Alternative approaches to fabricating lead-free joints, including spot welding and cold-pressing, have also been investigated. These methods have the potential advantage of achieving direct NbTi-NbTi joints with no intermediate, lower performance superconducting material. The spot welding method produced joints with the best superconducting performance, signifiantly better than the currently used PbBi solder, but the lack of reproducibility in this technique may be a problem from an industrial point of view.
12:45 PM - EP13.5.09
Electromechanical Energy Conversion in System with Bulk High-Temperature Superconductor
Ekaterina Kurbatova 1,Pavel Kurbatov 1,Pavel Dergachev 1,Yurij Kulayev 1
1 National Research University quot;Moscow Power Engineering Institutequot; Moscow Russian Federation,
Show AbstractThe features of the conversion of energy in linear vibration electromechanical device consisting of permanent magnet, coil with current and the element of the high-temperature superconducting material (HTS) are considered in the paper. The mathematical model for the calculation of the dynamics of the device and the method for determining the parameters of the models based on the analysis of the electromagnetic field are proposed. The mode in which an element of the HTS material is cooled in a magnetic field of the permanent magnet (field cooling (FC) mode) is research. Combined models of nonlinear, anisotropic and hysteretic properties of HTS materials containing current density and magnetization are composed. The approximating functions of the specific electrical resistance of the HTS and its relative permeability are built by hyperbolic functions, taking into account the critical values of the magnetic field, the volume current density and temperature. For the calculation of the electromagnetic field the method of spatial integral equations was applied.
The developed models and methods of calculation of electromagnetic systems and electromechanical converters with HTS elements are confirmed by experimental results. The results of calculations, theoretical and experimental research of the model structure of the electromechanical convertor with HTS elements are compared with the parameters of devices without HTS. The analysis of the amplitude-frequency and phase- frequency characteristics of the currents and vibration velocity, dependences of electrical and mechanical powers on frequency, dependences of the complex electrical and mechanical power, phase of current and efficiency on the mechanical load. The research is showed that the bulk HTS elements significantly change the parameters of the process of conversion of electrical energy into mechanical energy. There is a significant change of the impedance of the converter, currents, powers, vibration amplitudes and efficiency in a wide range of variations of the oscillation frequency and the load resistance.
Construction elements of bulk HTS materials increase efficiency and power density, so electromechanical converters with bulk HTS elements can be more effective than traditional designs, but for the successful design further improvement of the mathematical apparatus of modeling of processes and properties of HTS materials is required.
This article was prepared with inputs from work carried out in priority areas of the Russian Science Foundation "Fundamental research and exploratory research by individual research groups", project number 14-19-01458 "Research and modeling of bulk electrical properties of high-temperature superconducting (HTS) materials, development of methods for the analysis of electromagnetic fields of new types of magnetic systems of electrical devices with HTS elements"
EP13.6: Tailoring Materials III
Session Chairs
Anna Palau
Chiara Tarantini
Thursday PM, March 31, 2016
PCC North, 200 Level, Room 226 B
2:30 PM - *EP13.6.01
Development of Iron-Based Wires and Tapes for High-Field Applications
Yanwei Ma 1
1 Inst of Electrical Eng CAS Beijing China,
Show AbstractIron-based superconductors, with Tc values up to 55 K, are of great interest for applications, due to their lower anisotropies and ultrahigh upper critical fields. In this talk, we first review the current methods for transport Jc enhancement in iron-based superconducting wires and tapes by the powder-in-tube process, with a focus on the 122 family pnictide tapes. For applications, besides high Jc, there are many other performance requirements for wires, here we show some recent results of developing additional functions for practical 122 tapes, such as scalable techniques, multifilament, mechanical strength and low cost etc. we also present the results on the first 11 m long 122 tape fabricated by the scalable rolling process.
3:00 PM - *EP13.6.02
Superconductivity and Crystal Structures in Hydrothermally Synthesized FeX and [(Li,Fe)OH]FeX (X = S, Se)
Ursula Pachmayr 1, Juliane Stahl 1,Dirk Johrendt 1
1 Chemistry LMU Muenchen Muenchen Germany,
Show AbstractIron chalcogenides FeX (X = S, Se) with the tetragonal anti-PbO type structure represent the archetypal iron based superconductors and exhibit a striking range of critical temperatures between 4.5 K in FeS up to 100 K in thin FeSe films.The properties of the FeX compounds strongly depend on the synthesis procedure: Low-temperature hydrothermal reactions yield superconducting FeS, but non-superconducting FeSe, while the opposite is true for high-temperature solid-state methods. We have found that FeSe from hydrothermal reactions is triclinic in contrast to orthorhombic FeSe from solid-state synthesis [1]. This may be responsible for the absence of superconductivity. However, the reason why the low temperature structures are different is still not understood. On the other hand, superconducting FeS remains tetragonal at low temperatures. The absence of a structural transition suggests that nematic spin or orbital ordering is not present in FeS.
The intercalated iron chalcogenides [(Li,Fe)OH]FeX (X = S, Se) are exclusively accessible though hydrothermal reactions at temperatures around 180°C. The selenide exhibits superconductivity up to 43 K which, remarkably enough, co-exists with ferromagnetic ordering of the iron moments in the [(Li,Fe)OH] layer below 10 K [2]. Replacing selenium for sulphur in [(Li,Fe)OH]FeSe1-xSx gradually suppresses superconductivity, while the ferromagnetism persists [3].
[1] U. Pachmayr, N. Fehn and D. Johrendt, Chemical Commun. in press, (arXiv:1509.04851)
[2] U. Pachmayr, F. Nitsche, H. Luetkens, S. Kamusella, F. Brückner, R. Sarkar, H. Klauss, D. Johrendt, Angew. Chem. 54, 293 (2015).
[3] U. Pachmayr and D. Johrendt, Chemical Commun. 51, 4689 (2015).
3:30 PM - EP13.6.03
Stability of (Ba1-xKx)Fe2As2 in Contact with Water Vapor and Oxygen
Yesusa Collantes 1,J. Weiss 2,Yong Liu 3,Thomas Lograsso 3,E. Hellstrom 1
1 Applied Superconductivity Center National High Magnetic Field Laboratory, Florida State University Tallahassee United States,2 Department of Physics University of Colorado Boulder United States3 Division of Material Sciences and Engineering Ames Labaratory, US DOE Ames United States4 Department of Materials Science and Engineering Iowa State University Ames United States,3 Division of Material Sciences and Engineering Ames Labaratory, US DOE Ames United States
Show AbstractAlthough there have been reports of stability issues with 122 materials in air, there are no studies that address this topic. Studying the stability of (Ba1-xKx)Fe2As2 (K-doped Ba-122) superconductors in contact with water vapor and oxygen is important to design protocols on how to store samples to ensure reproducibility between measurements. Also, it may help elucidate the formation of extrinsic defects in these materials that are detrimental to their superconducting properties. This study was conducted on K-doped Ba-122 single crystals and polycrystalline samples with compositions x = 0.40 (optimally doped) and 0.60 (over-doped). Our objective was to understand what drives the degradation of K-doped Ba-122, how the samples degrade, and whether the degradation occurs on the surface or in the bulk. To do this, we analyzed changes in magnetic susceptibility and critical current density (Jc) as a function of time for samples stored under different conditions for 11 weeks. The storage conditions were: in air (O2 and moisture), in a desiccator (O2 and reduced moisture), and in an argon atmosphere glovebox (reduced O2 and reduced moisture). There were no changes in the critical temperature (Tc) or critical current density (Jc) for single crystals stored in any of the storage conditions. Polycrystalline samples stored in air showed a systematic decrease of Tc with increasing exposure time, from 31 K to 28.5 K for optimally doped sample and from 24.5 K to 19 K for over-doped sample. In these same samples, Jc was reduced by a factor of 2 for optimally doped and by a factor of 8 for the over-doped polycrystalline samples. There were no significant variations in Tc and Jc for polycrystalline samples stored in dry air and argon. These results revealed that moisture is the main factor for degradation in Ba-122. We will discuss how moisture degrades Ba-122, degradation products, where the degradation mainly occurs, and how to store samples to avoid degradation and have reproducibility between measurements.
3:45 PM - EP13.6.04
The Conditions for Achieving High Self-Field Critical Current Densities at 77 K in 25 mol.% Zr-Added (Gd,Y) Ba2Cu3Ox Superconductor Tapes
Meysam Heydari Gharahcheshmeh 1,Eduard Galstyan 1,Aixia Xu 1,Yuan Zhang 1,Jaideep Kukunuru 1,Rahul Katta 1,Goran Majkic 1,Xiao-Fen Li 1,Venkat Selvamanickam 1
1 Department of Mechanical Engineering and Texas Center for Superconductivity Univ of Houston Houston United States,
Show AbstractThe conditions for achieving high in-field critical current densities (JC) above 15 MA/cm2 at 30 K, 2.5 T (B||c) in REBa2Cu3O7-δ (REBCO and RE=Gd, Y) superconductor tapes with Zr content of 20-25 mol.% have been determined. In this work, heavily-doped REBCO tapes were fabricated by Metal Organic Chemical Vapor Deposition (MOCVD) using a reel-to reel process. The optimal compositional range of REBCO superconductor tapes with Zr content of 25 mol.% obtained by Inductively Coupled Plasma (ICP) has been determined to achieve the critical current densities above 3.5 MA cm−2 at 77K in zero applied magnetic field. The latest improvements in self-field critical current density and critical temperature of 25 mol.% Zr-added REBCO tapes will be discussed in this presentation.
This work was supported the Advanced Research Projects Agency-Energy, Office of Naval Research and Argonne National Laboratory
4:30 PM - *EP13.6.05
Light-Ion Modification and Masked Ion Beam Structuring of YBa2Cu3O7-d Thin Films
Johannes Pedarnig 1,Wolfgang Lang 2,Georg Zechner 2,Lisa Haag 2,Florian Jausner 2,Meirzhan Dosmailov 1,Marius Bodea 1
1 Institute of Applied Physics Johannes Kepler University Linz Austria,2 Faculty of Physics University of Vienna Vienna Austria
Show AbstractThe electrical and superconducting properties of high-Tc superconducting (HTS) YBa2Cu3O7-d (YBCO) thin films are tailored by the introduction of point defects upon irradiation with light ions at low energy. The YBCO films are grown by pulsed-laser deposition technique and the irradiation is performed employing a (collimated) beam of 75 keV He+ ions. The resistivity in the normal state and the critical temperature Tc of c - axis oriented YBCO films are systematically varied with increasing irradiation dose. On vicinal YBCO films the in-plane and out-of-plane resistivity is measured and the resistivity anisotropy decreases with increasing dose. Masked ion beam structuring (MIBS) is performed by irradiating YBCO films through stencil masks. MIBS results in local modification of the electrical and superconducting properties of YBCO and structures smaller than 100 nm in size are produced. The superconducting order parameter is suppressed in irradiated nanostructures. Magnetoresistance and critical current in YBCO films that are MIBS patterned with a square array of dots (300 nm spacing) show distinct features at commensurate arrangements of magnetic flux quanta with the artificial defect lattice.
Acknowledgements: This work was supported by the European Science Foundation (COST Action MP-1201, Research Network ‘Nanoscience and Engineering in Superconductors NES’) and by the European Erasmus Mundus program.
5:00 PM - *EP13.6.07
New Strategies for Engineering Pinning Landscapes in CSD YBCO Nanocomposites
Anna Palau 1,Ferran Valles 1,Alexander Stangl 1,Mariona Coll 1,Pablo Cayado 1,Bernat Mundet 1,Jaume Gazquez 1,Josep Ros 2,Susagna Ricart 1,Xavier Obradors 1,Teresa Puig 1
1 Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) Bellaterra, Barcelona Spain,2 Universitat Autonoma de Barcelona Bellaterra, Barcelona Spain
Show AbstractThe fabrication of nanostructured YBCO thin films by the incorporation of nanosized oxide secondary phases has been shown to strongly enhance their pinning performances, ensuing great potential for use in a broad number of power applications. It is now clear that different nanoparticle (NP) characteristics, growth processes and conditions lead to a rich zoology of defects in the film, whose effectiveness depends on the magnitude and orientation of the magnetic field and the temperature. We have demonstrated that the huge isotropic pinning forces obtained in CSD nanocomposites arise from the strains associated to intergrowths emerging from the NPs [1]. Moreover, natural defects of many types such us, vacancies, staking faults or twin boundaries my act as pinning centers, as well.
Here we present our present understanding of an extensive research on CSD nanocomposites prepared following two different approaches. On First, the in-situ approach, where adding metalorganic salts in the precursor solution, different randomly-oriented NP (BZO, BYTO, YO2 and mixed) are segregated. The second approach named ex-situ is a radically new concept consisting on the incorporation of prefabricated NP colloids (CeO2, ZrO2, CoFe2O4, BZO) in the solution to have much better control of the NP characteristics.
Only with the full knowledge of the correlation between vortex pinning and nanostructure in this complex materials, will allow to specific nano-engineering the pinning landscape for best superconducting performances. In this contribution, we report on a variety in-situ and ex-situ YBCO nanocomposites where processing conditions has enabled us to control the density, length and stoichiometry of intergrowth emerging from oxide nanoparticles. The synergetic combination of natural and engineered defects in these complex systems will be evaluated by means of in situ angular transport measurements and high resolution STEM.
Symposium Organizers
John Durrell, University of Cambridge
Luisa Chiesa, Tufts University
Kazumasa Iida, Nagoya University
Takanobu Kiss, Kyushu University
Marina Putti, Università di Genova
Symposium Support
ESAS European Society for Applied Super Conductivity
JECC TORISHA Co., Ltd.
Research Institute of Superconductor Science and Systems, Kyushu University
EP13.7: Tailoring Materials IV
Session Chairs
John Durrell
Kazumasa Iida
Friday AM, April 01, 2016
PCC North, 200 Level, Room 226 B
9:30 AM - *EP13.7.01
Progress on Pinning Enhancement in AMSC's 2G HTS Wire
Martin Rupich 1,Srivatsan Sathyamurthy 1,Qiang Li 2,Vyacheslav Solovyov 2,Ulrich Welp 3,Wai-Kwong Kwok 3,Maxime Leroux 3,Leonardo Civale 4,Serena Eley 4
1 American Superconductor Corp Devens United States,2 Brookhaven National Laboratory Upton United States3 Argonne National Laboratory Argonne United States4 Los Alamos National Laboratory Los Alamos United States
Show AbstractThe performance of the Second Generation (2G) high temperature superconducting (HTS) wire based on YBa2Cu3O7−δ (YBCO) has improved to the point that it is now being used in fault current limiter and cable applications; however, its use in coil-based applications for rotating machines is limited due to the steep reduction in critical current in the presence of an external magnetic field. Efforts to improve the pinning on 2G wire have focused on the introduction complex defect structures that act as vortex pinning centers. The most effective pinning landscapes have been based on aligned BaMO3 (M = Zr, Hf, Nb, etc.) nano-rods formed by self-assembly during vapor phase deposition of YBCO films along with rare-earth nanoparticles. However, these complex pinning landscapes haven proven difficult to control in long length production processes and are not applicable to the solution-based YBCO growth process used by AMSC. Thus we have been exploring alternate routes to incorporate precisely engineered defect structures into production length MOD-based REBCO films. One promising approach is the formation of point defects in the YBCO film by ion irradiation. Research over the past year has shown that the addition of point defects produced by irradiation can significantly enhance the pinning in the MOD-based REBCO films, with the critical current (Ic) more than doubling at ~30K in magnetic fields >2.5 T. The defect microstructure and pinning enhancement can be tuned by the choice of ion, energy and dosage and can be optimized for the specific operating temperature and field. In addition, the process is applicable to reel-to-reel manufacturing. In this presentation, we will review potential performance enhancements demonstrated in short R&D samples and production length 2G wires.
10:00 AM - EP13.7.02
Correlated Study of Local Ic Variation and Microstructural Disorder in a Bi-2223 Long Tape by Use of Hybrid Microscopy: Scanning Hall-Probe Microscopy and X-Ray Tomography
Takanobu Kiss 1,Kohei Higashikawa 1,Masayoshi Inoue 1
1 Kyushu Univ Fukuoka Japan,
Show AbstractSpatial homogeneity is one of the most important requirements for practical HTS tapes and/or wires since fluctuated critical current, Ic, possibly induces thermal instability or deterioration of reliability of HTS devices. To screen out such local Ic degradation, reel-to-reel transport measurement is often used with a voltage tap distance of around 1 m in commercial Bi-2223 long tapes. In fact, recent commercial products achieve good homogeneity with a standard deviation of Ic less than 1 % with transport Ic of 200 A in a length of hundreds of meters. In this study, we carried out spatially resolved measurement on local Ic variation in a commercial 100 m-long Bi-2223 multi-filamentary tape by use of reel-to-reel scanning Hall-probe microscopy (RTR-SHPM). By using a reel-to-reel wire traveling system, we magnetize the tape in a liquid nitrogen bath, then measured magnetization by use of a fast scanning Hall-probe sensor. The maximum speed of the measurement was 36 m/h with a longitudinal resolution of 1 mm. Such high resolution measurement allows us to visualize discrete local Ic drop of 20-25 % in the long tape. Statistical analysis of the Ic distribution shows that the probability of such Ic drop of 20 % was less than 0.1 %. Therefore, the standard transport measurement cannot detect such infrequently localized Ic drops. To investigate the origin of such Ic variation, we also carried out microstructural analysis by use of X-ray tomography. This allows us to visualize 3-dimensional internal filament structure with a spatial resolution of 2 μm with non-destructive manner. Correlated study between SHPM and X-ray tomography showed that the Ic drop was originated from deformation of the alignment of filament bundle. This result suggests that rolling process has a room to be improved to realize further highly uniform long tapes.
Acknowledgements: This study was supported by the “JST: S-Innovation” and "JSPS: KAKENHI (24360122)”.
10:15 AM - EP13.7.03
Magnetization Relaxation and E-J Characteristics in a REBCO Coated Conductor with BaHfO3 Artificial Pinning Centers
Yuta Onodera 1,Kazutaka Imamura 1,Takumi Suzuki 1,Kohei Higashikawa 1,Masayoshi Inoue 1,Akira Ibi 2,Tomo Yoshida 2,Takato Machi 2,Teruo Izumi 2,Takanobu Kiss 1
1 Kyushu University Fukuoka Japan,2 ISTEC-SRL Kanagawa Japan
Show AbstractIn a REBCO coated conductor based magnet winding, the tape strand itself induces large magnetic moment because of its flat and wide monolithic superconducting layer. Such magnetic moment shows relaxation also due to flux creep effect. This magnetic moment distorts field homogeneity and temporal stability of magnetic field in the magnet. It is relevant issue to understand dynamic behavior of such magnetization relaxation at various operation conditions. In this study, we investigated magnetic moment relaxation in a PLD process REBCO coated conductor introduced with BaHfO3 artificial pinning centers. The magnetic moment was measured by a SQUID magnetometer. To study the influence of critical condition, i.e., the ratio between induced magnetization current density and critical current density, Jc, we have investigated the behavior at step-cooling condition. The sample was first magnetized at 67 K, and then cooled down to 65 K with step-wise temperature profile during the relaxation. The relaxation is suppressed by the step-cooling, however, by the time when the relaxation curve approaches to that of original 65 K without temperature change, the decay starts again. From the relaxation measurement, we also obtained electric field-vs.-current density (E-J) characteristics. It has been shown that the change of the relaxation rate can be clearly explained by the shift of E-J characteristics by the operation temperature. This indicates that it is possible to know the dynamic behavior of the relaxation by the E-J characteristics. Experimental results have been describe analytically within the framework of percolation transition model taking into account Jc distribution and thermal fluctuation [1]. The relaxation behavior around 35K and the temperature dependence of the pinning potential will also be discussed.
This work was partly supported by the "METI and AMED: Development of Fundamental Technology for HTS Coils" and "JSPS: KAKENHI (24760235)”.
[1] T. Kiss et al., Physica C 392-396 (2003) 1053-1062.
10:30 AM - *EP13.7.04
Roebel Assembled Coated Conductor (RACC) Cables as Candidate for Future Accelerator Magnet HTS Inserts – Expectations and Requirements
Anna Kario 1,Simon Otten 1,Andrea Kling 1,Bernd Ringsdorf 1,Brigitte Runtsch 1,Alexandra Jung 1,Wilfried Goldacker 1
1 ITEP KIT Karlsruhe Germany,
Show AbstractIn the framework of EU program: ’’Enhanced European Coordination for Accelerator Research & Development’’ – in the project EuCARD2 and its work-package 10 – future magnets, i.e. a demonstrator accelerator dipole magnet using high-temperature superconductors (REBCO-HTS-tapes) is under development. The expectations for the magnet demand a high-current low-loss HTS cable instead of single conductors. The requirements on the cable properties are: a large current to allow low enough coil impedance by reducing the number of turns in the magnet quality issues for a precise field pattern, good bending tolerance and resistance to high Lorentz forces. Among different high-temperature superconducting cable concepts, only the RACC cable provides full transposition of strands and a very high engineering current density. It was therefore selected as the most suitable cable for the magnet demonstrator.
In this contribution, different key development issues of RACC cables for accelerator magnets are discussed. The crucial and important parameters that determine suitability for punching into the meander structure will be considered. Also, the influence of tape architecture as well as macro- and microstructural defects on punched strand quality will be shown. The optimized architecture of the cable itself and modification of its architecture to meet the demands of accelerator magnets will be outlined and discussed. Further, precision and reliability of the punching process for long length RACC production (up to 40 m) will be addressed. The precision und uniformity of the cable strands is influenced not only by tool properties, but also by the tape homogeneity. Results on cable properties as bendability will be shown using different HTS tapes from different suppliers. The RACC cable is as flexible as a single tape in out-of-plane bending direction and shows no Ic degradation down to 7 mm bending radius, which easily fulfills the requirements of the coil design in the EuCARD2 challenge. All addressed topics are part of the RACC cable optimization for the final demonstrator of the HTS dipole magnet insert.
11:30 AM - *EP13.7.05
The Strain Irreversibility Cliff in Nb3Sn RRP® Wires, Its Origins, and Its Implications
Najib Cheggour 1
1 University of Colorado/NIST Boulder United States,
Show AbstractNb3Sn superconducting wires made by the restacked-rod process (RRP®) have reached very high critical-current performances that make them the prime candidates for use in the luminosity upgrade of the Large Hadron Collider (LHC). In a recent study, we revealed a precipitous change in the intrinsic irreversible strain limit eirr,0 of RRP® wires with heat-treatment temperature. This behavior, named the strain irreversibility cliff (SIC), happens over a temperature window of less than 20 °C in width, with the major part of the cliff (i.e. 0.05 % ≤ eirr,0 ≤ 0.3 %) occurring over a window of 10 °C or less. This abrupt transition of Nb3Sn filaments from a highly brittle state where they crack as soon as they are subjected to a tensile strain of any measurable amount, to a more resilient state where they exhibit a remarkable elastic behavior up to a tensile strain as high as 0.4 %, raises a number of questions concerning the root cause(s) for crack initiation and propagation in Nb3Sn material. In this presentation, we will provide full description of SIC in RRP® wires either doped with Ti or Ta, and discuss its possible origin(s). We will also examine its significance on the fabrication of magnets for the LHC upgrade, and discuss its repercussions on the heat-treatment optimization and on the trade-off between the wire’s critical-current density and residual-resistivity ratio.
12:00 PM - *EP13.7.06
Practical HTS 2G Wire: Performance, Price & Utilizing Ways
Seung-Hyun Moon 1
1 SuNAM Co., Ltd Anseong Korea (the Republic of),
Show AbstractLong-length GdBCO coated conductors (CCs) possessing high critical current at 77 K in self field up to ~800 A/cm-width are being produced via a reactive co-evaporation deposition and reaction (RCE-DR) process by SuNAM Co. in Korea. Due to a very high conversion rate from an amorphous precursor film into the GdBCO film, an overall processing speed for producing the GdBCO film is faster than 120 m/h upto 1 km length. To achieve higher performance, better uniformity & higher production yield of GdBCO CCs, we have developed various kinds feedback control & inspection tools. Details of these methods will be explained, and also discuss the relations between price & yield, throughput.
Partly because of very fast conversion speed of RCE-DR process, a relatively weak pinning property has been the most challenging problem. Thus, in order to overcome this problem, we have tried to refine Gd2O3 particles trapped in the GdBCO matrix with varying the composition. In this talk, detailed pinning effects of theses pinning centers & modified phase diagram with non-stoichiometric case will be presented.
HTS 2G wire is a stacked thin tape form & have lots of different aspects comparing with multi filamentary conventional LTS round wire. So in many applications HTS 2G wire gives a lots of difficulties, but we can find the different ways of utilizing its strong points. We’ll show the some results of such a way, and discuss the future prospects.
* This work was supported by a grant from the Power Generation & Electricity Delivery Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) funded by the ministry of Trade, Industry and Energy (MTIE).