Oxidation and Reduction of Bi2Sr1.85Cuo6-Y Crystals

AbstractThe effects of oxidizing and reducing atmospheres on the oxygen contents and electrical properties of Bi2Sr1.85CuO6‐y single crystals were investigated. As‐grown crystals were normally semiconducting but became metallic and superconducting after heating the crystals for several hours in oxygen at temperatures between 500 and 800°C Previously superconducting crystals were made semiconducting by heat treatments in helium at temperatures between 700 and 780°C. Changes in the oxygen content of the crystals as well as the oxidation and reduction kinetics during the various heat treatments were monitored using standard thermogravimetric techniques. A good correlation was found between the annealing temperatures in oxygen (helium) at which there was an uptake (loss) of oxygen by the crystals, 500°C (700°C), and the onset (loss) of metallic behavior and superconductivity. From isothermal measurents of the weight change as a function of time, it was found that the apparent activation energies for oxidation and reduction were about 0.5 eV and 2.7 eV, respectively. A partial decomposition of the crystals during the various heat treatments, however, precluded a quantitative analysis of the kinetic data.

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Effect of oxygen content on the electrical properties of YBa2Cu3O7−x single crystals

Bulletin of Materials Science ◽

10.1007/bf02744720 ◽

1991 ◽

Vol 14 (3) ◽

pp. 753-758

Author(s):

B Ya Kotyuzhanskii

Keyword(s):

Electrical Properties ◽

Single Crystals ◽

Oxygen Content ◽

Effect Of Oxygen

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The stability of dislocation networks under various oxygen-doping conditions in superconducting Bi2Sr2CaCu2Oy single crystals and their influence on the flux pinning properties

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171742 ◽

1994 ◽

Vol 52 ◽

pp. 802-803

Author(s):

Y. Feng ◽

X. Y. Cai ◽

R. J. Kelley ◽

D. C. Larbalestier

Keyword(s):

Single Crystals ◽

Oxygen Content ◽

Basal Plane ◽

Flux Pinning ◽

Pinning Centers ◽

Before And After ◽

Anomalous Peak ◽

Basal Plane Dislocation ◽

The Stability ◽

Further Development

The issue of strong flux pinning is crucial to the further development of high critical current density Bi-Sr-Ca-Cu-O (BSCCO) superconductors in conductor-like applications, yet the pinning mechanisms are still much debated. Anomalous peaks in the M-H (magnetization vs. magnetic field) loops are commonly observed in Bi2Sr2CaCu2Oy (Bi-2212) single crystals. Oxygen vacancies may be effective flux pinning centers in BSCCO, as has been found in YBCO. However, it has also been proposed that basal-plane dislocation networks also act as effective pinning centers. Yang et al. proposed that the characteristic scale of the basal-plane dislocation networksmay strongly depend on oxygen content and the anomalous peak in the M-H loop at ˜20-30K may be due tothe flux pinning of decoupled two-dimensional pancake vortices by the dislocation networks. In light of this, we have performed an insitu observation on the dislocation networks precisely at the same region before and after annealing in air, vacuumand oxygen, in order to verify whether the dislocation networks change with varying oxygen content Inall cases, we have not found any noticeable changes in dislocation structure, regardless of the drastic changes in Tc and the anomalous magnetization. Therefore, it does not appear that the anomalous peak in the M-H loops is controlled by the basal-plane dislocation networks.

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