Interplane redistribution of oxygen in fine-grained HTSC

Abstract

Mössbauer spectra ( T = 78 and 293 K) and X-ray ( T = 293 K) studies of fine-grained high-temperature superconductors (HTSC) YBa 2Cu 2.985 57Fe 0.015O y ( y = 6.92–6.93, T c = 91–91.5 K) with the average grain sizes 〈 D〉 equal to 0.4, 1, and 2 μm are carried out. The redistribution in the intensities of Mössbauer spectra components with the decrease in the average grain size 〈 D〉 is found. The latter evidences the oxygen content to increase in (CuO δ ) basal planes at the expense of its decrease in (CuO 2) and (BaO) planes. The redistribution of the oxygen between the different planes of the unit cell is accompanied by the decrease in the lattice parameter c . These effects are caused likely by nonequilibrium conditions which are commonly used in preparation of fine-grained HTSC. The assumption about the existence of partial disorder between Y 3+ and Ba 2+ sites in the samples explains the observed changes in the values of δ and c parameters. An efficiency of Mössbauer spectra studies for the compounds of YBaCuO type in the case of the enhanced oxygen parameter δ and the possibility of its quantitative estimation from the analysis of the intensities of Mössbauer spectrum components is demonstrated.