HIGH-TEMPERATURE STUDY OF YTTRIUM-BARIUM-COPPER OXIDES NEAR THE YBA2CU3OX COMPOSITION BY IN-111 CD TIME DIFFERENTIAL GAMMA-GAMMA PERTURBED-ANGULAR-CORRELATION SPECTROSCOPY/

The local atomic order around very dilute indium impurities in c-axis- oriented YBa2Cu3O7 and YBa2Cu3O6.25 films at room temperature and in Y Ba2Cu3Ox bulk powders held in air or oxygen over a wide temperature ra nge were investigated using In-111/Cd gamma-gamma perturbed angular co rrelation (PAC) spectroscopy. The probe atoms occupy a single substitu tional lattice position in YBa2Cu3Ox, and evidence reported here stron gly supports previous claims that this is the yttrium position. In YBa 2Cu3Ox powders, the local atomic order changes continuously with tempe rature. At room temperature the electric field gradient measured by PA C in bulk YBa2Cu3Ox powder is indistinguishable from that in the fully oxygenated YBa2Cu3O7 him. Near the decomposition temperature, the bul k YBa2Cu3Ox powder data are semiquantitatively similar to data in the room temperature YBa2Cu3O6.25 film, with quantitative differences that we attribute to temperature averaging in the former. Other sites usua lly found in PAC spectra of YBa2Cu3Ox bulk samples arise from In-111 d issolved in Y2BaCuO5 and Y2Cu2O5 impurity phases. The latter phase app arently arises because of significant barium loss during processing; t he barium deficiency is clearly demonstrated by comparison of PAC data with the alloy phase diagram above the decomposition temperature. PAC data on pure Y2Cu2O5 are reported here also.