SOLID-SOLUTION OF YBACUXCO2-XO5 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1) AND ITS INTERGROWTH WITH YBA2CU3O7

Solid-solution materials of YBaCuxCo2-xO5 (0 less-than-or-equal-to X less-than-or-equal-to 1) have been synthesized by solid-state reaction. Using the XRD and HREM techniques, their structures were determined to be related to the defect perovskite structure and have tetragonal unit cells with a almost-equal-to 3.88 and c almost-equal-to 7.52 angstrom. Annealing YBaCo2O5 in pure oxygen leads to a 3 X 3 X 1 tetragonal superstructure which can be eliminated by electron beam irradiation or by annealing the specimen in argon, implying the existence of excess oxygen in the yttrium layer. A model for this superstructure with a composition of Y9Ba9Co18O49 has been suggested and supported by computer simulations of the HREM images. Irregular intergrowth of YBaCo2O5 and YBa2Cu3O7 has also been observed from a specimen with a nominal composition of Y2Ba3Cu3Co2O12.