bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Phase Diagram and Superconducting Behavior of the Ba1-Xkxbio3 System
Authors: Jorgensen J. D. , Pei Shiyou , Hinks D. G. , Dabrowski B. , Richards D. R. , Mitchell A. W. , Zheng Y. , Marx D. T. , Sinha S. K. , Newsam J. M. , Vaknin D. , Jacobson A. J. 
Published: March 2011

AbstractWe have determined the crystal structures of five phases in the Bal-xKxBiO3 system for 0≤x≤0.5 and 10K≤T≤473K. Superconductivity occurs only in a cubic perovskite phase with the maximum Tc at the transition to an orthorhombic, Ibmm, phase. The commensurate structure of this orthorhombic phase, which involves only tilting of the Bi06 octahedra, provides no explanation for its non-metallic behavior. However, an incommensurate structural modulation, observed by electron diffraction, may provide a rationalization. Thus, the maximum Tc at the phase boundary may result from competition between superconductivity and a charge density wave. Further studies of the phase diagram at high temperatures, where controlled oxygen atmospheres are required, reveal an unusual reentrant formation of a potassium-containing impurity phase which explains the need for synthesis techniques that involve initially reacting in a reducing atmosphere, followed by oxygenation at lower temperature.
Studies of Oxyfluoride Analogs of Nd1.85Ce0.15CuO4: Preliminary Results
Authors: Vanderah T.A. , Osofsky M.S. 
Published: March 2011

AbstractSamarium‐based oxyfluoride analogs of the apparently “n‐type” 24 K superconductor, Nd1.85Ce0.15CuO4, were prepared. A series of compounds with general formula Sm2‐xCexCuO4‐yFy were prepared and characterized by X‐ray diffraction, bromo/iodometric titration, and measurements of electrical resistivity. Homogeneous superconducting phases have not yet been obtained; preliminary results and discussion of property trends are presented.
Superconductivity in the (Nd,Ce,Ca)2Cuo4-Z System
Authors: Sakurai Takeshi , Yamashita Toru , Ikegawa Sumio , Yamauchi H. 
Published: March 2011

AbstractWe have controlled the carrier (electron) density in Nd2CuO2 of the T’ structure by introducing both Ce and Ca into the Nd‐sites, and studied the superconducting transition temperature versus carrier density relationship. The phase relations in the (Nd1‐x‐yCexCay)2CuO4‐z system were studied by means of powder X‐ray dirfractron and electron‐probe micro‐analysis techniques. For the phase diagram of the (Nd1‐x‐yCexCay)2CuO4‐z system, the single phase field of the T’ phase was established. Samples of the (Nd0.9‐yCe0.1Cay)2CuO4‐z system with compositions included in the single phase field were synthesized. The carrier density in these samples was varied by controlling the Ca content. The Hall effect and DC resistivity were measured to elucidate the relation between Tc and the carrier density.
Superconducting Behavior of Tetragonal T ‘Eu2‐xCexO4±δ
Authors: Melim V. J. , Peng Weimin , Kimball C.W. , Dabrowski B. , Zheng Y. , Hinks D. G. 
Published: March 2011

AbstractEu2.xCexCuO4±δ (0 ≤ x ≤ 0.17) has been synthesized with the tetragonal T’ structure. AC susceptibility and resistance measurements show that Eu2‐xCexCuO4±δ becomes superconducting with τc∼13 K for x= 0.15 and 0.17, when prepared under reducing conditions. The 151Eu Mossbauer shift shows that the Euvalence falls into a narrow range near Eu 3+ . The temperature dependence of the Mossbauer absorption yields a Debye temperature of 319 K for the Eu ion in Eu1.85Ce0.15CuO4±δ
Superlattice Modulation in Nd2cuo4 and the Electron ‐ Doped Systems Nd2‐xCexCuO4 and Nd2CuO4‐xFx
Authors: James A. C. W. P. , Murphy D. W. , Chen C. H. , Werder D. J. , Chiang J. , Zahurak S. M. , Fleming R. M. , Batlogg B. , Schneemeyer L. F. 
Published: March 2011

Abstract
Oxygen Content Variation in Cation-Deficient and Chemically-Doped High-TC Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O Superconductors
Authors: Kao Y. H. , Song L. W. , Yao Y. D. , Tao Z. , Jones K. W. 
Published: March 2011

AbstractOxygen content in high‐Tc superconductors has been determined by using a charged particle activation method. Changes of oxygen content in Cu‐deficient Y‐Ba‐Cu‐O and Cu/Bi‐deficient Bi‐Sr‐Ca‐Cu‐O compounds were obtained and used as a basis for discussing the variations in other cation‐deficient materials.
X-Ray Absorption Studies of Vanadium-Containing Yba2Cu3O7
Authors: Tan Z. , Budnick J. I. , Chen W. Q. , Weinbergers B. R. , Lynds L. 
Published: March 2011

AbstractAttempted V substitution leads to small but observable lattice expansions of the YBa2Cu3O7 main phase but has little effect on the superconducting transition temperature. X‐ray absorption spectra at the AT‐edges of V, Cu and Y and L3‐edge of Ba have been measured on vanadium‐containing YBa2Cu3O7 to address the question of V substitution in this material. We found that only a small amount of V can substitute into the YBa2Cu3O7 structure. The excess V forms an impurity phase in which V is tetrahedrally coordinated with oxygens.
Calcium substituted Y‐Ba‐Cu‐O superconductors with enhanced Tc
Authors: Morris D. E. , Narwankar P. , Sinha A. P. B. , Takano K. , Shum V. T. 
Published: March 2011

AbstractThe Tc of 124 is enhanced by Ca substitution: CaxY(1‐x)Ba2Cu4Oy prepared at 200 bar at 930°C shows Tc = 89 K for x = 0.1. The 124 phase remains stable with Ca substitution at P(O2) ≥ 50 bar. For P(O2) = 2‐16 bar, Ca substitution stabilizes a tetragonal 123 phase CaxY(1‐x)Ba2Cu4Oy, which shows a Tc (87 K for x = 0.2) comparable to that of unsubstituted orthorhombic 123. The synthesis of CaT‐123 has been achieved in oxygen overpressure as small as 1 bar.
Processing of High Current Density Yba2cu3ox Superconductors
Authors: Selvamanickam V. , Salama K. 
Published: March 2011

AbstractA liquid phase processing method has been developed to fabricate oriented grained YBa2Cu30x samples with high current density. The current density in these samples, however, is sensitive to the microstructure which is controlled by processing parameters. Cooling rate through the peritectic temperature is found to be the most crucial factor in controlling the extent of grain orientation and in turn the bulk current carrying capacity. The evolution of the microstructure during the slow cooling process is studied by quench experiments at different temperatures. From microstructural analysis, the suitable temperature profile for the slow cooling process is chosen. Current density measurements across grains show a Jc in excess of 104 A/cm2. This implies that the weak link behavior of grain boundaries in polycrystalline superconductors can be suppressed to a considerable extent.
Synthesis of Cuprate Ceramic Superconductors by Oxidation of Rapidly Quenched Alloy Precursors
Authors: Luo J.S. , Michel D. , Chevalier J.‐P. 
Published: March 2011

AbstractWe have produced various high Tc superconductors by oxidation of rapidly quenched alloy precursors produced by planar flow casting. This method generally leads to reactive oxidized powders and improves homogeneity if there is a solubility domain in the liquid state for the alloy. The grain size distribution is often more uniform than that for specimens prepared by conventional methods from mixtures of constituent oxides and carbonates.
Highly Textured Superconducting Bi2Sr2CaCu2Oy Crystals Prepared by Unidirectional Solidification Processing
Authors: Shiohara Y. , Oyama T. , Nakagawa M. , Suga T. , Ishige K. , Izumi T. , Nagaya S. , Miyajima M. , Hirabayashi I. , Tanaka S. 
Published: March 2011

AbstractUnidirectional solidification processing, including Floating Zone Melting, Vertical Bridgman, and Laser Zone Melting methods for making high Tc superconducting oxides has been investigated. The effects of processing parameters, growth rate (R) and temperature gradient (G), on texture, morphology, and structures of unidirectionally grown crystals were investigated. Two different crystallization mechanisms were recognized, one is non‐equilibrium phase transformation under high GR conditions, and the other is due to local equilibrium phase transformation under low GR conditions. Strongly aligned structures were obtained at high G/R ratios with low GR value. The interrelation between the superconducting characteristics and textured structure produced were also discussed.
Phase Chemistry and Micro‐Structure of Directionally Solidified Bi2Sr2CaCu2O8
Authors: Chow H.M. , Jiang X.P. , Cima M.J. , Haggerty J.S. , Brody H.D. , Flemings M.C. 
Published: March 2011

AbstractCeramic rods of Bi2Sr2CaCu2O8 (2212) were directionally solidified by laser‐heated float‐zone crystal growth [1]. The microstructure of the resulting material can be controlled through variation of growth rate. The 2212 phase is Sr‐deficient, having an actual composition Bi2.5Sr2CaCu2.2Oy. At slow growth rates (0.2 cm/h), plane front growth produced highly textured samples of almost phase pure 2212, and pole figures show that the solidification front proceeds along the (200) axis of the 2212 grains. Faster growth rates produced dendritic growth and polyphase microstructures. At the fastest growth rate studied (16 cm/h), no 2212 phase was observed. Observations indicate that Bi2.5Sr2CaCu2.2Oy melts peritectically into (Sr1‐x.Cax.)14Cu24Oy and a Bi‐rich liquid.
Melt Processing of Bi-Ca-Sr-Cu-O Superconductors
Authors: Cronin J.P. , Aruchamy A. , Rosenfelder S. , Kim S.-J. , Uhlmann D.R. , El-Bayoumi O.H. , Andrews R.J. 
Published: March 2011

AbstractUnidirectional crystallization of melt processed 2122 and 2223 composition in the Bi-Ca-Sr-Cu-O system has been carried out. Crystallization was controlled by heating the glass or cooling the melt using a moving furnace and a stationary sample. Fairly large oriented crystalline specimens of 2122 phases were obtained by cooling from the melt in a shallow gradient furnace. Glassy samples processed under steep gradients showed better crystallinity than those processed under shallow gradients.
Evolution of the High TcPhase in Rapidly Solidified Bi-Ca-Sr-Cu Oxides
Authors: Asthana A. , Han P.D. , Xu Z. , Chang L. , Payne D.A. , Gilbert P.J. 
Published: March 2011

AbstractMaterials in the system Bi-Ca-Sr-Cu-O were prepared by rapid solidification. Emphasis was placed on optimizing processing conditions for enhancement of the high Tc(2223) phase. A number of starting compositions and heat-treatments were investigated. The effect of dopants (such as, Pb, Sb, Ge, Sn) on the stabilization of the high Tc phase was evaluated. Small amounts of Pb and Sb were effective in significantly increasing the 2223 yield. Improvements in superconducting properties as a function of 2223 evolution are discussed with reference to SEM, TEM, XRD and SQUID results.
Effect of Oxygen Partial Pressure on Stability of High-Tc Phase in Sintered Bi-Pb-Sr-Ca-Cu-O Superconductos
Authors: Lee H.K. , Lee K.W. , Ha D.H. , Park J.C. 
Published: March 2011

AbstractThe effect of oxygen partial pressure on stability of high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system has been investigated using x-ray diffraction, resistivity and a.c. susceptibility measurements. It was found that part of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system was transformed into the low-Tc phase (80 K) and insulating phases by heating in the temperature range 600 C to 880°C in O2 of one atmosphere. The original high-Tc phase was restored upon retreatment in a low oxygen partial pressure of 0.1 atmosphere. The reversible superconducting phase transformation is discussed in conjunction with the formation mechanism of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system.
Reproducible, Large-Scale Production of Thallium-Based High-Temperature Superconductors
Authors: Gay Richard L. , Stelman D. , Newcomb J. C. , Grantham L. F. , Schnittgrund G. D. 
Published: March 2011

AbstractThe Rocketdyne Division of Rockwell International has developed a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique.In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination.Bulk samples of thallium-based powder were prepared by spray calcination, collected, cold-pressed, and sintered. An optimized temperature schedule was developed to produce T12Ba2Ca2Cu3Ox. Samples were examined by X-ray diffraction and characterized by measurements of critical transition temperature, Tc. A complete transition to zero resistance at 112 K was measured.
Luminescence from Defects and Impurity Centers in Y2O3
Authors: Jahan M. S. , Cooke D. W. , Bennett B. L , Hults W. L , Maez M. A. , Ott K. C. , Smith J. L. 
Published: March 2011

AbstractHigh-purity (99.999%) Y2O3 powder is used as a starting material for fabricating high-temperature superconductors (HTS), and is frequently found as an unreacted second phase in the final product. We have found that as-received Y2O3 contains Tb3+ paramagnetic impurity ions as determined by TSL and emission-spectra measurements. Deep luminescence traps (presumably Tb4+ ions) are formed in Y2O3 when it is exposed to frays, x rays, or fluorescent lights. These deep traps can only be removed by annealing the material to near 1600°C. Given the short coherence length of HTS it is possible that order-of-magnitude variations in the Tb impurity concentration of starting materials may affect the ultimate value of surface resistance (Rs).
Soft X‐Ray Studies of Y‐Ba‐Cu‐O Thin Films Prepared by Laser Ablation
Authors: Krol A. , Sher C.J. , Storch D.R. , Song L.W. , Kao Y.H. , Witanachi S. , Zhu Y.Z. , Patel S. , Shaw D.T. , Smith G.C. 
Published: March 2011

AbstractAngular variation of x‐ray fluorescence due to oxygen atoms in high‐T Y‐Ba‐Cu‐O thin films is measured for the first time by using a new parallel plate avalanche chamber. This technique allows the possibility of nondestructive probing of the depth‐profile of oxygen atoms in the superconducting materials. Our preliminary results indicate that the near surface region of the Y‐Ba‐Cu‐O film may contain an oxygen‐depleted layer of thickness around 20 nm.
High Tc Superconducting Bi-(Pb-)Sr-Ca-Cu-O Films Deposited by Pulsed Nd:Yag Laser Ablation
Authors: Levoska J. , Hagberg J. , Pusa P. , Uusimäki A. , Leppävuori S. 
Published: March 2011

AbstractHigh To superconducting Bi-(Pb-)Sr-Ca-Cu-O thin films were ablated on MgO(l00) substrates at room temperature using a Nd:YAG laser at 1064 or 532 nm. The target materials had compositions near Bi2-xpbxSr2Ca2+yCu3+zOy (x<0.6, y,z<l) and their zero resistivity temperatures were 101 - 105 K. The amorphous films were crystallized either by annealing near 850°C or they were first melted and then annealed. The effects of laser ablation parameters and annealing conditions were investigated. The films were studied by XRD, SEM/EDS and resistivity measurements.The best films were annealed near 850 °C and they consisted mainly of the 2223 phase. These films had T9(midpoint) at 107 K and zero resistivity at 100 K. In the melt-treated films the amount of the 2223 phase as well as Tc was lower. The superconducting phases in the annealed films were strongly oriented with their c-axes perpendicular to the substrate surface.
Thin Film Processing for High-Tc Superconductors of Bi-System
Authors: Wasa K. , Adachi H. , Hirochi K. , Ichikawa Y. , Setsune K. 
Published: March 2011

AbstractBasic thin film deposition processes for the high-Tc superconductors of Bi-systems are described. There appear several superconducting phases including the low-Tc phase Bi2Sr2Ca1 Cu2Ox and the high-Tc phase Bi2Sr2Ca2Cu3Ox. Thin films with these superconducting phases are synthesized by a selection of the substrate temperature Ts during the deposition : the high-Tc phase with Tc=100K is synthesized at Ts>800 °C; the low-Tc phase with Tc=80K, at Ts<600°C. However, these films often comprise show structure comprizing the different superconducting phases.The close control of the superconducting phase has been achieved by the layer-by-layer deposition in the atomic layer epitaxy process.
Synthesis and Properties of Ultra-Thin YBa2Cu3O7 and YBa2Cu3O7/La2-xSrxCuO4 Multilayers
Authors: Eom C.B. , Streiffer S.K. , Sun J.Z. , Yamamoto K. , Laderman S.S. , Bravman J.C. , Geballe T.H. 
Published: March 2011

AbstractUsing our standard single target off-axis sputter deposition procedure[1], ultra-thin YBa2Cu3O7 superconducting films were made in-situ. We have studied the thickness dependence of superconducting properties (Tc, Jc) from 20 to 5000Å. Tc starts degrading below 125Å and falls to 50 K for the 30 Å film. Jc drops linearly with decreasing thickness below l000Å. We have grown YBa2Cu3O7/La2-xSrxCuO4 superconducting thin film multilayers in-situ by the same process. The modulation wavelength of the multilayers ranged from 45Å to 2000Å. X-ray diffraction and cross sectional TEM confirm the superlattice periodicity. The superconducting transition temperature drops in much the same way as the single layer ultra-thin films. Both the critical current density and its magnetic field dependence decrease as the modulation wavelength decreases.
In‐situ growth of yba2cu3o7‐x films by metal organic chemical vapor deposition using vertical, high‐speed rotating disk reactor.
Authors: Noh D. W. , Gallois B. , Li Y. Q. , Chern C. , Rear B. , Tompa G. S. , Norris P. , Zawadzki P. 
Published: March 2011

AbstractSuperconducting thin films of YBa2Cu307‐x were grown on MgO (100) and YSZ(IOO) substrates without post‐annealing by metal organic chemical vapor deposition using vertical, high‐speed (1100 rpm) rotating disk reactor. The source materials were Y(tmhd)3, Ba(tmhd)2, and Cu(tmhd)2, which were kept at 135 °C, 240 °C, and 120 °C respectively. The precursors were transported using nitrogen as the carrier gas and introduced separately into the cylindrical stainless steel reaction chamber, which was maintained at 60 torr. The oxygen partial pressure was 30 Torr. The substrates were heated resistively at 800°C. After growth, the films were cooled down at a rate of 5 °C/min under 1 atmospheric pressure of pure oxygen. The X‐ray diffraction pattern of the films showed primarily an orientation of c‐axis perpendicular to the substrates, with weak peaks of (hoo) corresponding to a‐axis orientation. Scanning Electron Microscopy of the films showed a well‐developed a‐axis and c‐axis plate‐like structure which appeared as rectangular micron‐sized features on the MgO surface. On the YSZ substrates a‐axis and c‐axis plate‐like projections were also observed, with the dense plate‐like c‐axis orientation dominant. Four probe resistance measurements showed Tc(R=0) at 91.8 K(△TC=2.2 K) and 85 K (△TC=7 K) on YSZ and MgO substrates respectively.
Rapid Chemical Vapor Deposition of Yba2cu3ox Coatings
Authors: Lackey W.J. , Carter W.B. , Hill D.N. , Barefield E.K. , Hanigofsky J.A. , Shapiro M.J. , Moss III T.S. , Green A.J. , O'Brien D.F. , Jake R.A. , Efferson K.R. 
Published: March 2011

AbstractA rapid, controllable process for CVD of superconducting Yba2Cu30x has been developed. The new process relies on slowly feeding and pneumatically transporting powdered solid reagents directly into the CVD furnace; vaporizers are not used. Deposition rates two orders of magnitude greater than those achievable by reagent sublimation have been obtained using a powder feed mixture of Y, Ba, and Cu tmhd complexes (tmhd is tetramethylheptanedionate). Potentially, the process is applicable to thermally unstable, less volatile, lower cost reagents such as the acetylacetonates.
Lou Temperature Growth of Superconducting Ybaacu,07‐X Thin Films by Metalorganic Chemical Vapor Deposition
Authors: Kanehori Keiichi , Sugii Nobuyuki , Miyauchi Katsuki 
Published: March 2011

AbstractThin YBa2Cu307‐xfilms were grown by thermal and plasma enhanced MOCVD, and the effects of growth teiperature on the film properties were studied. The crystal Iinity of the fills deteriorated with growth teiperature, so superconductity decreased with growth teiperature. Thin fills grown by therial MOCVD at 600°C, 650°C, 700°C and 750°C had zero‐resistivity at 10K, 71K, 83K and 84K, respectively. The growth teiperature for superconducting fids is decreased by plasia enhancement. Thin films grown by plasma enhanced MOCVD at 515°C and 580 °C had zero‐resistivity at 60K and 85K. The critical current density of fills grown by plasia enhanced MOCVD at 580°C was 105A/cm2 at 77K.
Low Temperature Preparation of y‐bA‐cU‐0 Films by Omcvd
Authors: Tsuruoka Taiji , Kawasaki Ryodo , Abe Hitoshi , Shibata Susumu 
Published: March 2011

AbstractBy using N2O for oxygen source, Y‐Ba‐Cu‐O films prepared at 650” C on the SrTiO3 substrates showed zero resistance at 79K. The deposition rate of Y‐Ba‐Cu‐0 films on MgO(l00) substrates by using N2O gas was nearly half of that using 02 gas. X‐ray diffraction patterns of Y‐Ba‐Cu‐0 films grown on SrTiO3(100) and MgO(l00) substrates indicate c‐axis orientation.
Athermochemical Investigation of the La-Sr-Cu-O System
Authors: Bularzik Joseph , Navrotsky Alexandra , Scott Bruce , Bringley Joe , Trail Steve 
Published: March 2011

AbstractThe perovskite related La2‐xMxCuO4‐y oxides substituted with alkaline earth metals were one of the first classes of high temperature superconductors discovered. Determining the thermodynamic properties is important to understand the stability and superconducting mechanism of these structures. High temperature solution calorimetry, using a molten lead borate solvent, has been performed on La2CuO4 and the related Sr substituted oxides. Calorimetric measurements on CuO, La2O3 and SrCO3 yield heats of formation. A change in the trend of the heats of formation appears at Sr content 0.1, the reported orthorhombic to tetragonal transition, the onset of superconductivity and loss of oxygen.
Tem Study of Cvd‐Grown Bi‐Sr‐Ca‐Cu‐0 Thin Films on (001) Mgo Substrates
Authors: Ueda O. , Kimura T. , Yamawaki H. , Ihara M. , Ozeki M. 
Published: March 2011

AbstractCVD‐grown Bi‐Sr‐Ca‐Cu‐0 thin films on (OOl)MgO with T at 110 K have been investigated by transmission electron microscopy. The films are found to consist of large domains oriented along the c‐axis, with diameters of 15‐100 um. These domains exhibit incommensurate superstructures along the fa‐axis. In addition, we have observed similar superstructure spots in two equivalent directions normal to each other. It has also been found that the interface between the thin film and the substrate is very abrupt. Five different perovskite‐related layers along the c‐axis with different thickness are present. In the thin film, 80K phases are dominant and 110 K phases are less likely. Three other phases are very rarely observed. Furthermore, boundaries where the layered structure is different on both sides are often found.