Aging of the microstructure of melt-textured YBa2Cu3O7/Y2BaCuO5 composites and implications on their superconducting properties

Abstract

The aging process of the microstructure and superconducting properties of YBa2Cu3O7/Y2BaCuO5 directionally solidified composites has been observed upon increasing the oxygenation time. The process is characterized by an increase of the dislocation density up to a maximum of 1.3×1010 cm−2 and the formation of large stacking faults, preferentially from low-angle grain boundaries and around Y2BaCuO5 precipitates, as well as an intense degradation of the YBa2Cu3O7 matrix at either side of the microcracks and around the precipitates. The stacking faults propagate more easily along the 〈100〉 directions and the shear component of their associated displacement vectors is exchanged between the a and b axis directions at every twin boundary. Both stacking faults and matrix degradation occur along the (001) planes, giving rise to a pronounced two-dimensionality of the aged microstructure. The aging of the microstructure is accompanied by a strong field-dependent reduction of the critical currents leading to a downward shift of the irreversibility line. Low-field ac susceptibility measurements with H∥ab confirm an enhanced two-dimensional behavior associated with the layered defective microstructure. It is shown that the rate at which these layered defects are generated depends on the content of Y2BaCuO5 phase in the samples.

Source-reported materials — not catalogue approval

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