Showing papers by "Maw-Kuen Wu published in 1994"
TL;DR: It is found that the temperature dependence of the dc susceptibility follows the Curie-Weiss law in the temperature range 20--300 K and the paramagnetism of the Pr and [ital R] sublattices exist independently of one another.
Abstract: We conducted a detailed study of the structure and magnetic properties of ([ital R][sub 1[minus][ital x]]Pr[sub [ital x]])Ba[sub 2]Cu[sub 3]O[sub 7] sintered samples, where [ital R]=Lu, Yb, Tm, Er, Y, Ho, Dy, Gd, Eu, Sm, and Nd for [ital x]=0.5--1.0. We found that the temperature dependence of the dc susceptibility follows the Curie-Weiss law in the temperature range 20--300 K and the paramagnetism of the Pr and [ital R] sublattices exist independently of one another. The antiferromagnetic ordering temperature [ital T][sub [ital N]] of Pr ions decreases monotonically with increasing [ital R] concentration (1[minus][ital x]). At a given [ital x], [ital T][sub [ital N]] is [ital R]-ion-size dependent. The slope in the [ital T][sub [ital N]] vs [ital x] curve is steeper for ions with smaller ionic radii. The observed results are interpreted in terms of the hybridization between the local states of the Pr ion and the valence-band states of the CuO[sub 2] planes.
34 citations
13 citations
TL;DR: In this paper, the effects of Ag 2 O on the formation of the high-Tc Bi-Pb-Sr-CaCu-O phase were investigated.
Abstract: The effects of Ag 2 O on the formation of the high-Tc BiPbSrCaCuO phase were investigated. The slopes for the formation of high-Tc phase are about 0.39 and 1.56 for BPSCCO and BPSCCO/Ag 2 O pellets, respectively. On the other hand, the results also indicated that the addition of Ag 2 O in the samples reduced the partial melting temperature and strongly enhanced the formation of high-Tc phase in a lower sintering temperature (831°C).
11 citations
TL;DR: The structure of Ba1-xKxBiO3 has been investigated by triple-crystal X-ray scattering on a variety of single crystals of different compositions as mentioned in this paper.
Abstract: The structure of Ba1-xKxBiO3 has been investigated by triple-crystal X-ray scattering on a variety of single crystals of different compositions. Attention has focused on the modulation observed by electron diffraction in the (110) directions. None of the incommensurate reflections observed in such studies have been observed with X-ray scattering, evidence that such observations are caused by electron-beam-induced damage. However, superlattice reflections have been observed at (hk0) half-integer positions, evidence of a larger supercell due to the presence of a charge density wave caused by the ordered disproportionation between nonequivalent Bi(III) and Bi(V) ions. This commensurate modulation exists in both semiconducting (x 0.37) compositions.
9 citations
TL;DR: In this paper, the authors combined the electrophoretic deposition technique and the jelly-roll process to fabricate Bi-Pb-Sr-Ca-Cu-O (BPSCCO)/Ag tapes.
Abstract: We combined the electrophoretic deposition technique and the jelly-roll process to fabricate Bi-Pb-Sr-Ca-Cu-O (BPSCCO)/Ag tapes. A thick film of BPSCCO on an Ag substrate was prepared by electrophoretic deposition. The BPSCCO/Ag sheet was rolled up to the jelly-roll configuration and then cold rolled to form tape with six superconducting layers. The critical current density of the tape determined by magnetic measurement at 5 K in a 0.2 T field was about 6.5*104 A cm-2 and decreased to 1.3*104 A cm-2 near 5 T.
7 citations
TL;DR: In this paper, a low-Tc phase was dominant in a powder calcined at 800°C for 10 h along with a small amount of a very low Tc phase and some nonsuperconducting phases.
6 citations
TL;DR: In this paper, the authors investigated the effects of starting powder on the expansion of Bi-Pb-Sr-Ca-Cu-O pellets with various high Tc phase contents and sintered at 853 °C.
Abstract: We investigate the effects of starting powder on the expansion of BiPbSrCaCuO pellets with various high Tc phase contents and sintered at 853 °C. The starting BiPbSrCaCuO powders, with various high Tc phase contents and prepared by the different calcined conditions, strongly influenced the expansion behaviours of the BiPbSrCaCuO pellets. The expansion of these pellets decreased with increasing high Tc contents. The relationship among the expansion behaviours, formation of high Tc phase and gas release from the pellet during sintering are discussed in this paper.
5 citations
TL;DR: In this paper, a new structure, namely YBCO/CeO 2 /YSZ/MgO, was proposed to obtain in-plane rotation of 45°.
Abstract: It is difficult to obtain 100% bi-epitaxial 45° grain boundary junctions of YBCO using previously known structures. We have developed a new structure, namely YBCO/CeO 2 /YSZ/MgO and YBCO/MgO boundary, so that 100% in-plane rotation of 45° can be routinely obtained.
4 citations
TL;DR: In this article, single crystals of the Bi-2212 phase were grown by the travelling solvent floating zone method using Bi2.9Sr2.6Ca1.3Cu2Ox as solvent.
Abstract: Single crystals of the Bi-2212 phase were grown by the travelling solvent floating zone method. Steady growth can be readily achieved when Bi2.9Sr2.6Ca1.3Cu2Ox was used as solvent. Optimized starting composition and growth conditions for the growth of pure 2212 phase were determined. The as-grown 2212 phase crystal exhibits a zero resistance state at 82K with a narrow transition width (ΔTc=3K). Some of the crystals grown from a stoichiometry 2212 composition contained a high volume fraction of 2223 phase (with Tc, onset at 113K).
4 citations
TL;DR: In this article, a novel synthetic route to the formation of less air sensitive fullerene superconductors by mixing oxygen-containing alkaline compounds with C60 has been discovered.
Abstract: A novel synthetic route to the formation of less air sensitive fullerene superconductors by mixing oxygen‐containing alkaline compounds with C60 has been discovered. A high‐resolution single‐crystal x‐ray study on the K‐doped samples shows that the ratio of potassium to C60 is not 3:1. The observed stability enhancement and the off‐stoichiometry of potassium content may originate from the presence of oxygen which serves as an oxidative agent.
4 citations
TL;DR: In this article, a low-temperature anodic electrocrystallization method in a sodium hydroxide molten flux was used to obtain a plate-like La 2-x Na x CuO 4 crystal with 32 K superconductivity.
Abstract: Crystalline La 2- x Na x CuO 4 was obtained by a low-temperature anodic electrocrystallization method in a sodium hydroxide molten flux. A 2 h experiment can produce plate-like crystals with 0.1 mm×0.1 mm facets in a - b -direction and 32 K superconductivity as-grown.
TL;DR: In this article, coprecipitation with 8-hydroxyquinoline (oxine) as the precipitant was used to prepare the YBa 2 Cu 3 O y -Ag composites.
TL;DR: In this article, single crystals of YBa2Cu3O6 + δ, completely separated from flux, measuring up to 5-6 mm2 and 0.25-0.5 mm thick, were grown reproducibly from BaCuO2 solutions containing 0.8 wt% Ta2O5.
TL;DR: In this article, a superconducting YBa 2 Cu 4 O 8 sample with Tc=80 K has been obtained after heat treatment at 820°C. Characterization of the sample by X-ray diffraction, thermal analysis, electrical resistivity, magnetic susceptibility are reported.
Abstract: YBa 2 Cu 4 O 8 has been prepared by a solution-mix technique. The use of an appropriate complexing agent leads to a complete mixing of the Y 3+ , Ba 2+ and Cu 2+ cations. The superconducting YBa 2 Cu 4 O 8 sample with Tc=80 K have been obtained after heat treatment at 820°C. Characterization of the sample by X-ray diffraction, thermal analysis, electrical resistivity, magnetic susceptibility are reported.
TL;DR: In this article, a simple reciprocating rotation mechanism is described which can be used to rotate a crucible and/or a crystal in a crystal growing system, employing commercially available timer relays allowing accurate periods of motion and delay.
Abstract: A simple but versatile reciprocating rotation mechanism is described which can be used to rotate crucible and/or crystal in a crystal growing system. It employs commercially available timer relays allowing accurate periods of motion and delay in the rotation.
TL;DR: In this article, a series of samples with nominal compositions of La3CaxBa4−xCu7Oy, (0 ≤ x ≤ 4.00) was prepared by the solid state reaction method.
Abstract: A series of samples with nominal compositions of La3CaxBa4−xCu7Oy,(0 ≤ x ≤ 4.00) was prepared by the solid state reaction method. Single phase materials were obtained for 0 ≤ x ≤ 1.25 samples which had an oxygen stoichiometry, 16.021 ≤ y ≤ 16.587, equivalent to 6.866 ≤ z ≤ 7.109 per unit cell with a formula of La1.29Ca0.43xBa1.71−0.43xCu3Oz. An evidence of the hole doping was observed by substituting Ca ions for Ba ions. It was interesting that increasing the Ca substitution accompanied an increase in the oxygen stoichiometry to a maximum value of 7.109 with a hole concentration of 0.311 for x = 1.00 sample. A correlation between the Tc and the hole concentration was plotted and the result was very similar to that found in the YBa2Cu3O7−x superconductor.
TL;DR: In this article, coprecipitation using triethylammonium carbonate (Et 3 HN) 2 CO 3 ) as precipitant was used to prepare the YBa 2 Cu 3 O 7 (Y 1-2-3) and Y Ba 2 Cu 4 O 8 (Y 2-4) high-T c superconductive materials.
TL;DR: The fracture toughness of a single crystal of Ba0.62K0.38BiO3 was determined in this paper, where the Vickers microhardness measurements were made at room temperature for test loads between 50 and 2000 g for a peak load constant of 10 s.
TL;DR: In this article, a theoretical estimate of the conditions necessary for hydroxide coprecipitation and a preliminary characterization of the electron-doped cuprate, obtained after high-temperature treatment, are reported.
Abstract: Nd1.85Ce0.15CuO4- delta has been prepared from a diethylamine medium by the hydroxide coprecipitation method. A theoretical estimate of the conditions necessary for hydroxide coprecipitation and a preliminary characterization of the properties of the electron-doped cuprate, obtained after high-temperature treatment, are reported.
TL;DR: In this paper, a new route to the formation of less air sensitive fullerene superconductors using the mixture of C60 and Alkaline-metal carbonates was reported.
Abstract: We report a new route to the formation of less air sensitive fullerene superconductors using the mixture of C60 and Alkaline-metal carbonates. The materials so prepared contain oxygen in addition to the alkaline metal dopants. The alkaline metal content determined from single crystal x-ray is found to be 2.4 instead of the stoichiometry 3.
01 Jan 1994
TL;DR: In this paper, the effect of sintering temperature on the superconducting properties of BPSCCO bulk materials was studied by x-ray diffraction, scanning electron microscopy, and resistance measurement.
Abstract: Effect of sintering temperature on the superconducting properties of BPSCCO bulk materials was studied by x-ray diffraction, scanning electron microscopy, and resistance measurement. Experiments were carried out at 805-861°C for 48 hours in air. Results indicated that the sintering temperature had strong effect on the stablization of the high-Tc phase . It was found that the Tc reached 100-104 K with a sharp transition and almost contained a pure high-Tc phase after sintering at 825-852°C. The correlations of superconducting properties with microstructures of BPSCCO materials are discussed in this paper.
TL;DR: In this paper, the effect of starting powders, prepared by different heat treatment processes on the grain-oriented YBCO bulk materials, were studied by X-ray diffraction, scanning electron microscopy and a quantum design SQUID magnetometer.
Abstract: The effect of the starting powders, prepared by different heat treatment processes on the grain-oriented YBCO bulk materials, were studied by X-ray diffraction, scanning electron microscopy and a quantum design SQUID magnetometer. Results suggest that the specimens, which were calcined at 750° C for 10 h, heated at 950° C for 24 h, and then sintered at 930° C for 20 h, were preferentiallyc-axis oriented. The grain-orientation was found to be due to the partial melting of the YBCO compound.
01 Jan 1994
TL;DR: In this paper, the superconducting transition temperature, Tc, first decreases linearly with Sr-content until x>0.4 where a sharp drop in Tc occurs.
Abstract: We have achieved the preparation of the Y(Ba1−xSrx)2Cu3O7 compounds with x ranging from 0 to 1 by substituting small amount of Cu by Mo. It was observed that the superconducting transition temperature, Tc, first decreases linearly with Sr-content until x>0.4 where a sharp drop in Tc occurs. X-ray structure analysis shows that a sharp drop in Tc at a critical concentration corresponds to the crystal change from orthorhombic to tetragonal.
TL;DR: In this paper, the authors have achieved the preparation of the (Y 1-x Ca x )Sr 2 (Cu 3-y Fe y )O 7-δ (0.4≤y≤0.6) compounds.
Abstract: We have achieved the preparation of the (Y 1-x Ca x )Sr 2 (Cu 3-y Fe y )O 7-δ (0≤x≤0.2, 0.4≤y≤0.6) compounds. The transition temperature increases linearly with increasing Cu(1)-O(1) distance and decreasing Cu(2)-O(1) distance. It was also observed that Tc increases with the carrier concentration on the CuO plane(P sheet ).