bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Formation of Y-Ba-Cu-O Phases During Solid State Reaction
Authors: Chin T. S. , Huang T. W. , Lin W. T , Wu N. C. , Chou Y. H. , Wu T. C. , Wu P. T. , Yen H. H. 
Published: March 2011

ABSTRACTThe formation of Y-Ba-Cu-O phases, including the high Tc superconducting YBa2Cu3O7−x (Y123) phase, during solid state reaction of the mixture of Y2O3: BacO3: CuO, in molar ratio of 0.2:0.6:1 to conform the formula of the perovskite (Y0.4 Ba0.6)CuO3 composition was studied by means of DTA, DTG and X-ray difractometry(XRD). For continuous heating at 10 C/min, it was found that the Y123 phase exists at 790–995 C, and gradually disappears at higher temperatures. The insulating Y2BaCuO5 (Y211) phase exists at 985 to 1190 C, the maximum experiment temperature. While the semiconducting YBa3Cu2O7-y, (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate temperature and time for the formation of the Y123 phase is 900 C and 16 hours. Semiquantitative data on the amount of phases presented, including the above mentioned phases and other binary Ba-Y-O or Ba-Cu-O phases, during heating are also given. High temperature superconductor with a Tc of around 93 K can be synthesized reproducibly by the processes based on this study.
Effect of Thermal Processing on the Microstructures and Superconducting Properties of YBa2Cu3Oy
Authors: Gotoh K. , Enomoto H. , Iida K. , Takano Y. , Mori N. , Ozaki H. 
Published: March 2011

ABSTRACTThe effect of thermal processing in the sample preparation of YBa2Cu3Oy has been investigated systematically on microstructures and electrical properties. The grain size was found to grow preferably during the cooling process rather than during the sintering process. The high Tc superconducting phase appears around 500 C in this thermal processing. The annealing experiment shows that the grains still grow at low temperature such as 300 °C.
Processing - Property Relations in YBa2Cu3O6+x Superconductor
Authors: Safari S. A. , Wachtman J. B. , Parkhe V. , Caracciolo R. , Jeter D. , Rao A. S. , Sundar H. G. K. , Jisrawi N. , McLean W. L. 
Published: March 2011

ABSTRACTProcessing of YBa2Cu3O6+x superconducting samples by employing different precursor powder preparation techniques such as ball milling, attrition milling and also narrow particle size distribution powder preparation through coprecipitation by spraying will be discussed. CuO coated with oxalates shows the lowest resistance above T up to room temperature. The extent of corrosion by water has been studied by employing magnetic susceptibility, XPS and X-ray diffraction. Superconducting samples are affected to a considerable extent when treated in water at 60° C and the severity of the attack increases with time.
Laser Induced Deposition of YBa2Cu3O7−x Thin Films
Authors: Kwok H. S. , Mattocks P. , Shaw D. T. , Shi L. , Wang X. W. , Witanachchi S. , Ying Q. Y. , Zheng J. P. , Bush P. 
Published: March 2011

ABSTRACTWe describe here the deposition of the YBCO superconducting thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed.
Effect of Oxygen Annealing on Low-Resistivity Contactsfor High-Tc Superconductors
Authors: Ekin J. W. , Panson A. J. , Blankenship B. A. 
Published: March 2011

ABSTRACTA method for making low resistivity contacts to high-Tc superconductors has been developed, consisting of depositing noble metal contact pads (silver or gold) on a clean superconductor surface at low temperatures (<150°C). After annealing the silver contact pads in oxygen at intermediate temperatures (<500°C) for one hour, contact resistivities less than 2 × 10'° Ω-cm2 at 76 K are obtained, about six orders of magnitude less than for indium-solder contacts. Before annealing, the contact resistivities are still very low, in the 10-6 to 10-5 Ω-cm range at 76 K, which would be useful when contacts with low fabrication temperatures are required. The voltage-current characteristics of the contacts are strongly nonlinear after annealing, having a superconducting transition character. This is ascribed to the critical current of the superconducting material being exceeded at the contact interface. External connections to the contact pads have been made using both solder and thermosonic wire-bonding techniques.
Interface Effects of Laser Ablated and Sputtered High Tc Superconducting Thin Films
Authors: Dam B. , Baller T. S. , Van Veen G. N. A. , Van Hal H. A. M. , De Vries J. W. C. , Stollman G. M. 
Published: March 2011

ABSTRACTHigh Tc superconducting thin films were prepared by DC triode sputtering and laser ablation. With both deposition methods we were able to fabricate thin films on SrTiO3 which show an onset at Tcf=92 K. The superconductive transition is complete at Tcf=86 K. On other substrates like Al2O3, MgO and ZrO2 relatively poor results were obtained.
Formation of thin film YBaCuO Superconductors from Cu/BaO/Y2O3 Layer Structures
Authors: Chang Chin-An , Tsuei C. C. , Chi C. C. , Scheuermann M. R. , Yee D. S. , Berosh J. P. 
Published: March 2011

ABSTRACTThin film superconductors of the YBaCuO family have been fabricated using layer structures of Cu/BaO/Y2O3 deposited by electron-beam evaporation. Using layer thicknesses off the stoichiometric YBa2Cu3O7, we have formed superconducting films with zero resistance above 77°K using MgO and SrTiO3 substrates. The films were found to be composed of both the superconducting YBa2Cu3O7 phase, and the non-superconducting green Y2BaCuO7 phase. Dependence of transition temperatures on the annealing temperatures and the substrates has also been studied.
Preparation of Y-Ba-Cu-O Superconducting Films by Modified Dc Sputtering Process
Authors: Lin R. J. , Chen Y. C. , Kung J. H. , Wu P. T. 
Published: March 2011

ABSTRACTHigh Tc Y-Ba-Cu-O superconducting thin films have been successfully deposited by DC sputtering techniques with excellent adhesion properties. Onset temperature of 95K had been achieved without any heat treatment nor annealing. Typical deposition rate is 1–2A/sec. It is possible to fabricate the superconducting thin films on a variety of substrates with this techniques, i.e., SiO2, Si and MgO. Analysis indicated that the films were predominantly the orthorhombic perovskite structure with traces of copper oxide.
Preparation of thin Film YBa2CU3O6+X Ceramic Superconductors by the Sol-Gel Process
Authors: Kramer S. , Wu K. , Kordás G. 
Published: March 2011

ABSTRACTHigh Tc superconducting powders and thin films on silicon have been fabricated by the sol-gel process. Both powder and film preparation involved the synthesis of metal alkoxides, followed by the complexation of yttrium, barium, and copper alkoxides in a common solvent. Bulk gels were then vacuum dried and fired at 700 and 950 °C in flowing oxygen. Thin films on (100) silicon were fired at 700 °C in flowing oxygen. Susceptibility vs temperature measurements showed that the thin films on silicon had a Tc of 40 K while the bulk gels fired under the same conditions had a Tc of 75 K. The sample fired at 950 °C was superconducting at 90 K.
Materials Aspects of Oxide Superconductors - Effect of Ambient Water on Superconductivity-
Authors: Kitazawa K. , Kishio K. , Hasegawa T. , Ohtomo A. , Yaegashi S. , Kanbe S. , Park K. , Kuwahara K. , Fueki K. 
Published: March 2011

ABSTRACTIt has been found that the chemical instability of Ba2LnCu3O7 causes some problems in the measurements of critical temperature and creates a highly resistive grain boundary contact which is the major cause of the low critical current density at the present moment. Firstly, measurements of the superconductive critical temperature could be seriously misled if based solely on resistive transition because apparent resistivity anomaly is observed due to electrochemical EMF which appears when the electrode contact is attacked by water. Secondly, the barrier nature of the grain boundary against charge carriers is significantly enhanced by the chemical attack of the boundary region with water and water/carbon dioxide in the annealing atmosphere. This leads to a further weakening of the Josephson weak link between polycrystalline grains in the high Tc oxide superconductors.
Thin Films of Y-Ba-Cu-O by Rf Sputtering
Authors: Ballentine Paul H. , Kadin A. M. , Árgana J. , Rath R. C. 
Published: March 2011

ABSTRACTThin films of Y-Ba-Cu-O have been prepared by rf diode sputtering from a single mixed-oxide powder target. The films were deposited on sapphire and cubic zirconia substrates, with the substrates either cooled, heated, or left to establish thermal equlibrium. The Cu content in the films decreased with increasing substrate temperature. Films having composition close to the desired 1–2–3 stoichiometry were fabricated either by enriching the target with CuO or by cooling the substrate. Using the latter approach, a single target was used for over 20 depositions yielding films that were uniform in composition (although slightly Cu-rich), and consistent from run to run. These films had as-deposited room temperature sheet resistances on the order of 100 kΩ. Subsequent annealing at temperatures up to 850 C resulted in films that were superconducting with an onset around 90 K and zero resistance at 50 K. The critical current was found to exceed 2000 A/cm2 at 4.2 K.
Magnetic Investigations of Superconductive, Polycrystalline (RE)1Ba2Cu3O7−x Compounds (RE = Y, Gd, Ho, Dy)
Authors: Thompson J. R. , Boatner L. A. , Brynestad J. , Christen D. K. , Kim Y. C. , Sales B. C. , Sekula S. T. 
Published: March 2011

ABSTRACTMagnetic properties have been investigated for several rare-earth based, polycrystalline samples of high Tc superconductive “123” compounds with magnetic onset temperatures between 90 and 95 K. Analysis of the susceptibility × of samples based on Gd, Ho, and Dy indicates that the superconductive and magnetic properties are independent of one another to a substantial degree. Studies of the critical current density Jc are reported.
Effect of Temperature Cycles on the Critical Current Density of YBa2Cu3O7-δ
Authors: Tiefel T. H. , Jin S. , Sherwood R. C. , Fastnacht R. A. , Nakahara S. , Fisanick G. , Boone T. 
Published: March 2011

ABSTRACTThe transport Jc of the polycrystalline YBa2Cu3O7-δ superconductor seems to be dominated by weak links between high Jc regions as evidenced by low Jc values and their strong field dependence. The possible effects of thermal expansion-contraction and the tetragonal-orthorhombic transformation on the weak links and the Jc values were investigated by repeated thermal cycling of sintered pellets between -196°C and various high temperatures (600–850°C) using a furnace heating and cooling in an oxygen atmosphere. While more than a five-fold decrease in Jc from -400 to -70 A/cm2 (at 77K in zero field) is observed after 5 temperature cycles between -196'C and 850°C, only a slight decrease (to -370 Atm2) is noticed after 5 cycles between -196*C to 600°C, the temperature span of which is not all that much smaller than the former cycles. Transmission electron microscopy analysis clearly indicates that the drastic deterioration in Jc by repeated phase transformation is caused by increased amount of microcracks on (001) basal planes near the grain boundaries. The results will be discussed in terms of the large thermal expansion anisotropy of this layer-structured compound.
Reentrant Softening in Copper-Oxide Superconductors
Authors: Violet C. E. , Datta T. , Ledbetter H. M. , Almasan C. , Estrada J. 
Published: March 2011

ABSTRACTOn the basis of our reentrant-softening model, sound-velocity results in La1.85Sr0.15CuO4 and YBa2Cu3O7−x are shown to be neither dissimilar nor inconsistent with thermodynamic requirements. In both materials, as temperature decreases, the lattice softens just above Tc. Below Tc, this softening is offset by increased stiffness associated with the developing superconducting phase. This model agrees with results from other physical-property measurements, and it predicts that elastic stiffness is higher in the normal state than in the superconducting state.
Changes in Microwave Absorbtion of New High Tc Superconductors with Small Magnetic Fields
Authors: Khachaturyan K. , Weber E. R. , Tejedor P. , Stacy A. , Portis A. 
Published: March 2011

ABSTRACTA low field microwave absorbtion peak was observed with an EPR spectrometer in the new superconducting oxides‥ The peak disappeared above the superconducting transition temperature after exponential decrease with temperature in the transition region. The peak was sensitive to the magnetic fields the sample has been exposed before in the superconducting phase. Magnetic field dependent stochastic oscillations of the EPR baseline are ascribed to flux trapping in Josephson junctions.
Penetration Depth Measurements of YBa2Cu3O7-δ at 4 MHz
Authors: Wiesmann H. , Corderman R. R. , Moodenbaugh A. R. , Ruckman M. W. , Strongin Myron 
Published: March 2011

ABSTRACTMeasurements were made of the penetration depth of bulk and powder samples of YBa2Cu3O7-δ. The samples were placed in an inductor which was part of the resonant circuit of a 4 MHz tunnel diode oscillator. The oscillator was stable to at least 1 part in 106 at 77 K. Changes in the sample susceptibility were easily detected by changes in the oscillator frequency. Analysis of the smallest powders fabricated gave a value of the measured penetration depth λmea = 0.23 μm. The measurement methodology is quantitative and the value of Xmea is believed to be an upper bound of the true penetration depth.
Radiation Damage in YBa2Cu3O7 by Fast Neutrons
Authors: Willis J. O. , Cost J. R. , Brown R. D. , Thompson J. D. , Peterson D. E. 
Published: March 2011

ABSTRACTThe superconducting transition temperature of sintered YBa2Cu3O7 decreases at a rate of 2.7 K/1018 n/cm2 (E > 0.1 MeV) for fast neutron irradiation. The critical current density Jc increases a factor of three at zero field and more than three at nonzero fields for fluences up to 2×1018 n/cm2. At both 7 and 75 K, Jc is decreasing with fluence near 3×1018 n/cm2.
Electronic Structure of Fluorine-Substituted YBa2Cu3O7 Superconductor
Authors: Ching W. Y. , Xu Yongnian , Wong K. W. 
Published: March 2011

ABSTRACTThe electronic structures of fluorine-substituted YBa2Cu3O7. crystals are studied by means of first-principles calculations. The most likely site of substitution is 0(1) and the most unlikely site is 0(4).
Critical Current Density Enhancement and Moisture Destruction Studies of the Compound Superconductor Y-Ba-Cu-Ag-O
Authors: Yao Y. D. , Krol A. , Krol Y. H. , Walters C. , Spagna S. , Althoff J. , Woronick S. , Jang L. Y. , Xu F. 
Published: March 2011

ABSTRACTWe have fabricated a series of samples of YBa2(Cu1−x Agx)3Oy compounds where 0 ≤ × ≤ 1, with the intention to study the changes in critical current density and the effect of moisture treatment on normal state resistance R in these high transition-temperature superconductors. The samples exhibited a decrease of the transition-temperature Tc vs the Ag concentration x. Tc is about 93 K for YBa2Cu3Oy and 20 KCfor YBa2Ag3Oy, but it is almost unaffected by the presence or Ag for × < 0.2. An enhancement of the critical current density Jc by nearly an order of magnitude for the samples with 0 < × ≤ 0.1 has been observed. Both Jc and R are found to be sensitive to the ambient moisture conditions.
Oxygen Vacancy Ordering in BaYCu3O7−x, 0 ≤ x ≤1, by Electron Diffraction Studies
Authors: Alario-Franco M. A. , Capponi J. J. , Chaillout C. , Chenavas J. , Mareziom M. 
Published: March 2011

ABSTRACTElectron diffraction photographs of Ba2YCu3O7−x with x ∼ 0.15, ∼ 0.50, and ∼ 0.85, show diffuse scattering which can be attributed to the partial ordering of the oxygen vacancies. For x ∼ 0.15 and ∼0.85 it consits of continous rods which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the unit cell 2√2ac × 2√2ac × 3ac. This cell is orthorhombic or tetragonal for x ∼ 0.15 and ∼ 0.85, respectively. For the former composition every fourth O4 atom is removed from every other CulO4 chain. For the later the ordering is the same, however, the occupied oxygen positions become vacancies, and vice versa. Both orderings are uncorrelated along the c axis. For x ∼ 0.5 the diffuse scattering consits of either continuous rods or continous ribbons which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the orthorhombic unit cell 2ac × ac × 3ac. The ribbon widths are sample dependent. For this type of compounds all O4 atoms of every other CulO4 chain running along the b axis, are removed. As in the previous cases the ordering is uncorrelated along the c* axis. The ribbon elongation along the a* axis is indicative of additional disorder along this axis. This disorder seems to be related to the oxygen stoichiometry.
Raman Scattering Studies on Superconducting YBa2Cu3O7−x, Semiconducting YBa2Cu3O6+x, and Possible Impurity Phases
Authors: Mascarenhas A. , Katayama-Yoshlda H. , Geller S. , Pánkové J. I. , Debt S. K. 
Published: March 2011

ABSTRACTA Raman spectroscopie investigation of specimens of superconducting YBa2Cu3O7−x and semiconducting YBa2Cu3O6+x indicates that in the range 100 to 700 cm-1, the characteristic lines of the superconductor at 13 K, are at 150, 338, 441, 507, 590, and 644 cm-1. Comparison of the Ranan spectra of the superconductor and the semiconductor indicates a mode stiffening of the pair at 338 and 441 cm-1, hut a mode softening of the pair at 507 and 590 cm-1. A factor group analysis leads to a tentative assignment of the Raman and infrared allowed modes. At temperatures 12K < T < 180K the Raman spectra of the superconductor indicate that the phonon mode at 338 cm-1 has an anomalous temperature dependence below the superconducting critical temperature (Tc).
Flux Trapped State Versus Glassy State in Superconducting BaErCuO and BaYCuTiO
Authors: Nam Sang Boo 
Published: March 2011

ABSTRACTThe temperature dependent magnetization, M(T), of superconducting BaErCuO and BaYCuTiO was measured via the BTi SQUID susceptometer. In the zero field cooling case, M(T) of BaErCuO was found to be similar to that of Pb. But, M(T) of BaYCuTiO was found to decrease rapidly with T and be almost linear in T. However, in the field cooling case the fluxoids were found to be trapped at all T below Tc, and its amount was found to depend on Ts at which the sample starts to be cooled, as observed in Pb. The ergodic limiting points were not observed within the chosen parameters. The irreversibility of magnetization observed in both BaErCuO and BaYCuTiO is attributed to the fluxoids, trapped during the field cooling process.
Effect of Oxygen Annealing on the Magnon-Pair Raman Scattering in La2CuO4-y
Authors: Ohana I. , Liu Y. C. , Dresselhaus M. S. , Dresselhaus G. , Strauss A. J. , Zeiger H. J. , Picone P. J. , Jenssen H. P. , Gabbe D. R. 
Published: March 2011

ABSTRACTPolarized Raman scattering spectra at 300K and 20K are reported for a single crystal of La2CuO4-y before and after annealing in oxygen at 1000°C for 24 hours. Oxygenation strongly quenches the temperature sensitive line at ∼1430 cm-1 (for T ∼ 300K) in the “as grown” crystal, previously identified with magnon-pair excitation associated with two-dimensional antiferromagnetic ordering. In addition, the phonon spectrum is greatly modified by the addition of oxygen, indicating a more uniform local crystalline environment after oxygenation. Raman scattering is thus a sensitive probe of the effect of oxygenation on the near surface magnetic and phonon properties of La2CuO4-y.
Derivative Analysis of the High Temperature Superconducting Transition
Authors: Almasan Carmen , Estrada J. , Poole C. P. , Datta T. , Farach H. A. , Gubser D. U. , Wolf S. A. , Toth L. E. 
Published: March 2011

ABSTRACTThe shape of the normalized temperature derivative of the dc susceptibility provides useful information about superconducting materials. We propose that the position of the derivative peak be defined as the transition temperature Tc and the width of this peak define its sharpness.
Calorimetric Studies of High Temperature Oxide Superconductors
Authors: Saito Yasutoshi , Nakamura Tetsurõ , Atake Tooru 
Published: March 2011

ABSTRACTThe heat capacities of single phase samples of Ba2DyCu3O7 and Ba2ErCu3O7 which were prepared by the method of powder-calcination have been measured over the temperature range 13–300 K by using a laboratory-made adiabatic calorimeter. A typical second-order type of anomaly was observed due to the superconducting phase transition at 92.5 K in Ba2DyCu3O7 and at 91.2 K in Ba2ErCu3O7. From the heat capacity jump at the transition temperature, the electronic heat capacity coefficient was estimated as 30 mJ·K-2.mol1 for Ba2ErCu3O7 and 32 mJ·K-2. mol-1 for Ba2ErCu3O7. Large differences were found in the low temperature heat capacities between the two samples, which were analyzed on the basis of Schottky-type of anomalies owing to the magnetic ions of Dy and Er.
Carrier Concentration amd High Tc Superconductivity
Authors: Karpe N. , Szymczak I. , Chen D.-X. , Sanchez A. , Nogues J. , Rao K. V. 
Published: March 2011

ABSTRACTA systematic study of the influence of oxygen depletion on the carrier concentration and the occurence of superconductivity in a single-phase 1–2–3 Y-Ba-Cu-Oxide material is presented. This is accomplished by successive measurements of the Hall and electrical resistivities, ac-susceptibility, and x-ray diffraction on the same sample, in which the oxygen deficiency is controlled and determined from thermogravimetry. With increasing oxygen depletion, we monitor how the 93K orthorhombic superconductor, with an estimated carrier concentration of 0.6·1022 carriers/cm3 at 100K, is transformed into a tetragonal semiconductor with a very low carrier concentration.
The Preparation of Bulk and Thick Films of YBa2Cu3O7-y Using a Solution Technique
Authors: Barboux P. , Tarascon J. M. , Bagley B. G. , Greene L. H. , Hull G. W. , Meagher B. W. , Eom C. B. 
Published: March 2011

ABSTRACTWe have synthesized the high Tc superconducting oxide YBa2Cu3O7-y using a solution technique and compare the resultant properties to materials synthesized by solid state reactions. Because the cations are mixed at the microscopic level, we observe that this solution technique allows lower reaction temperatures and shorter reaction times to obtain the superconducting material. They yield materials with particle sizes of about 1 μm and having a narrow size dispersion (as compared to the typically 50 μm particle sizes obtained by solid state reactions). The smaller, uniform particle sizes yield denser compacts upon sintering. Densities of 90% have been achieved and metallic-like behavior improves and is correlated with increasing density. The solution derived materials superconduct at 91 K and have narrow transition temperatures (0.6K width) which we attribute to sample compositional and structural homogeneity. Because we are able to produce stable, viscous gels, we have investigated the preparation of large area thick films on various substrates of technological interest (e.g. alumina, zirconia.strontium titanate).
Oxygen Stoichiometry in LA-BA-CU-O Perovskites
Authors: Sunshine S. A. , Schneemeyer L. F. , Murphy D. W. , Wasczcak J. V. 
Published: March 2011

ABSTRACTThe oxygen ordering and exchange properties of Ba2−xLa1+xCu3O7±δ and BaLa4Cu5O13±δ are detailed. The crucial role of oxygen ordering for superconductivity is described.
Ionic Models for YBa2 Cu3 O7
Authors: Wright N. F. , Painter G. S. , Busing W. R. , Butler W. H. 
Published: March 2011

ABSTRACTSimple ionic models are applied to YBa2 Cu3 O7. It is found that additional forces are needed to constrain the barium and the planar coordinated copper atoms to be stable in their observed positions. These additional forces are compared to forces calculated from first principles. It is observed that the restoring forces are small for motion of the “in chain” oxygen atoms perpendicular to the chains.