CRYSTAL STRUCTURES AND DEFECTS IN PHASES EXISTING IN Ba3Y2Cu5O15−x

Abstract

Crsytal structures and defects of the phases existing in Ba3Y2Cu5O15−x have been investigated with SAED, CBED and HREM. Sample A was furnace cooled and is a high Tc superconductor whereas sample B is air cooled and not superconducting at 77.35K. Both samples contain predominantly the so called superconducting phase with the space group Pmmm (a=0.386, b=0.389 and c=1.16 nm) and a minor phase, called phase-II with the space group Pbam (a=1.23, b=0.740 and c=0.571 nm). In sample B, the other three minor phases are: phase-III: orthorhombic, a=0.892, b=0.639 and c=0.535 nm; phase-IV: BCC, a=1.82 nm and phase-V: hexagonal, a=b=0.526, c=0.635 nm. The positions of the Ba, Y and Cu atoms can clearly be seen in the structural image viewed along the [100] direction of the superconducting phase. The contrast increment of the bright spots on the basal plane was perhaps related to the oxygen vacancies. Lattice distortion, (010) and [Formula: see text] domain boundaries in the superconducting phase, microdomains and twins in phase-III have been observed. High resolution electron micrographs of both phase-II and phase-IV were also presented. The amount of the superconducting phase and defects in the crystal structure may affect the superconductivity of the Ba3Y2Cu5O15−x oxide significantly, the former being bene-ficial and the latter harmful.