Showing papers by "Maw-Kuen Wu published in 1992"
TL;DR: In this paper, a normal metal sheet is configured in a jelly-roll fashion and cold worked into tapes or wires made of alternating cuprate superconductor and normal metal layers.
6 citations
TL;DR: The activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy have been measured by modified coulometric titration method in a temperature range from 913 to 957°C as mentioned in this paper.
Abstract: The activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy have been measured by modified coulometric titration method in a temperature range from 913 to 957 °C. The standard Gibbs formation energies and the diffusivity of oxygen in liquid Yb1Ba2Cu3 for 1/2O2 (1 atm)→O (1 at. %) are determined to be ΔG=−655.20+0.335T(K) (±1.5) kJ/mol and D=1.8×10−2 exp(−48 100/RT) (cm2/s) where R=8.314 J/deg×mol. Despite very strong bonding of oxygen to the liquid alloys, the diffusion coefficient of oxygen is relatively high in the order of 10−4 cm2/s. The solubility of oxygen in the liquid alloy is low, of about 0.0145 and 0.017 at. % at 913 and 935 °C, respectively.
2 citations
TL;DR: In this paper, the authors measured the activity and diffusivity of oxygen in liquid Ag•Yb1Ba2Cu3 and Tl1Ba•Ca•Cu3 at 930 and 900°C, respectively, by a modified coulometric titration method on the galvanic cell.
Abstract: We have measured the activity and diffusivity of oxygen in liquid Ag‐Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 at 930 and 900 °C, respectively, by a modified coulometric titration method on the galvanic cell: O_ in liquid alloys/yttria stabilized zirconia/air, Pt. The standard Gibbs formation energy and the diffusivity of oxygen in liquid Ag‐Yb1Ba2Cu3 alloy for 1/2O2(1 atm)→O_(1 at. %) are determined to be ΔG=−247.4 kJ/g atom, and D=1.52×10−4 cm2/s. The oxygen solubility Cs in the Ag‐Yb1Ba2Cu3 alloy is 0.0913 at. %, a factor of 5.5 higher than that in Yb1Ba2Cu3 alloy. The addition of Ag does not alter the growth mechanism and the oxygen diffusion controls the film growth. The growth speed is enhanced as a result of the enhanced oxygen solubility. ΔG and the diffusion coefficient of oxygen in the Tl1Ba2Ca2Cu3 liquid alloy are −257 kJ/g atom and 1.2×10−4 cm2/s, respectively. The oxygen solubility of the Tl1Ba2Ca2Cu3 alloy at 900 °C is found to be very high at ∼5.74 at. %. All thermodynamic data for oxygen in the precursor...
1 citations
TL;DR: In this article, a low temperature anodic electrocrystallization method in a potassium hydroxide molten flux was used to obtain bismuthate Ba1-xKxBiO3 with x greater than 0.5.
Abstract: Crystalline bismuthates Ba1-xKxBiO3 with x greater than 0.5 are obtained by a low temperature anodic electrocrystallization method in a potassium hydroxide molten flux. The x = 0.56 bismuthate crystal shows 8K superconductivity determined by AC magnetic susceptibility.
TL;DR: In this paper, a series of samples with a nominal composition of R3CaBa3Cu7Oy (abbreviated as R3137), where R = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm, was prepared by a similar process as for an 80-K superconductor.
Abstract: A series of samples with a nominal composition of R3CaBa3Cu7Oy (abbreviated as R3137), where R = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm, was prepared by a similar process as for an 80-K superconductor, La3CaBa3Cu7Oy. Most of the R3137 (except for R = Ce, Tb) had a tetragonal triple-perovskite phase like La3137 identified from the XRD patterns, and they were superconducting except Pr3137. For R3+ radius larger than Dy3+ (0.908 A), a single phase R3137 was observed, and their Tc(zero)' probably related to the rCu-o distance in the copper-oxygen layer, was spread from 85 to 76 K with a maximum for the Eu3137. Oxygen stoichiometry of these R3137 was slightly decreased with decreasing lanthanide radii. The hole concentration, (Cu-O), was found between 0.47 and 0.38/unit cell. For Smaller R3+ ions, residual resistivity was found in the superconducting samples due to the existence of second phase. From the structural study of La3137, it was known that part of the lanthanide ions had to be fitted into the bigger Ba-site. Because ionic radii of the heavy lanthanides (R3+ ≤ Ho3+ = 0.894 A) were too small to be located at the Ba-site, it was rather difficult to prepare these single phase R3137.
TL;DR: In this article, the authors carried out a systematic study of the detailed I-V characteristic in magnetic fields of the YBa2Cu3O7 (YBCO) single crystals and c-axis oriented thin films and derived critical exponents suggest the occurrence of 3D to 2D crossover of the flux motion.
Abstract: We have carried out a systematic study of the detailed I-V characteristic in magnetic fields of the YBa2Cu3O7 (YBCO) single crystals and c-axis oriented thin films. For all the samples studied, there exists a temperature at which the I-V satisfies simple power law. The I-V characteristic also follows the scaling behavior predicted by the phase transition model based on the random disorder. The derived critical exponents suggest the occurrence of 3D to 2D crossover of the flux motion. The critical field at which the crossover occurs depends on the sample thickness.