Mat. Res. Bull., Vol. 22, pp. 849-855, 1987. Printed in the USA. 0025-5408/87 $3.00 + .00 Copyright (c) 1987 Pergamon Journals Ltd. HIGH-TEMPERATURE SUPERCONDUCTIVITY IN YBa2Cu30 7 AND RELATED PEROVSKITE OXIDES: SOME ASPECTS OF SOLID STATE CHEMISTRY + C.N.R. Rao , P. Ganguly, K. Sreedhar, R.A. Mohan Ram and P.R. Sarode Solid State & Structural Chemistry Unit Indian Institute of Science Bangalore-560012, India, (Received April 20, 1987; Refereed) ABSTRACT Thermogravimetry and Cu "K-absorption edge measurements show that the superconducting YBa~Cu] 0 7 sample (annealed in 02 ) contains more oxygen than the nonsupe¥co~ducting sample annealed in-N2, the former has s less distorted structure with the actual composition not far from the ideal one. Oxides of the formula Yl-x Ba2Cu307 (x = 0.05, 0.10 and 0.15) annealed in oxygen also possess the perovskite structure and show high-T superconductivity. The superconduccting transition temperature seems Cto generally increase with the nominal Cu3+/Cu 2÷ ratio in the superconducting copper oxides. Control of the Cu3+/Cu 2+ ratio (and hence the density of states at the metal-nonmetal transition in the non-super- conducting state) through the oxygen stoichiometry or an appropriate cation substitution seems to provide a basis for synthesizing high-To copper oxides. MATERIALS INDEX: oxides, perovskites, barium, copper, yttrium Introduction Of the various high-temperature oxide superconductors reported in the last few weeks, the highest transition temperatures are found in members of the Y-Ba-Cu-O system (I-3). Based on a systematic x-ray investigation of composi- tions of the type Y3-x Ba3+xCu6014, we proposed (4,5) that the oxide responsible +Contribution No. 448 from the Solid State & Structural Chemistry Unit To whom all correspondence should be addressed. 849