Abstract
We have used the isothermal electric resistance relaxation to investigate the variation of microstructure and oxygen diffusion behaviour in melt-texture grown (MTG) YBCO bulk. Post-annealing below 550 °C for an as-grown sample does not seriously influence the grown defects except for oxygen deficiency, and the variation of electric resistivity during oxygenation below 550 °C is attributed to the variation of oxygen content in the Y123 matrix. Post-annealing at 930 °C reduces obviously the rate of the electric resistivity relaxation and the final value of the fully saturated electric resistivity due to the oxygenation at lower temperatures, which is attributed to the rearrangement of as-grown defects that are also partly annealed out, in the Y123 matrix at high temperature. The isothermal electric resistance relaxation due to oxygen uptake at 350–500 °C for MTG-YBCO bulk after post-annealing at 930 °C has been systematically investigated. The chemical diffusion parameters of oxygen were estimated under certain assumptions. Compared with reported data for Y123, the diffusion activation energy is in the low value range and the apparent chemical diffusion coefficient is in the high value range for MTG-YBCO. This is all attributed to the grown defects and their variation in MTG-YBCO.
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