Interplane redistribution of oxygen in fine-grained HTSC

Abstract Mossbauer spectra ( T  = 78 and 293 K) and X-ray ( T  = 293 K) studies of fine-grained high-temperature superconductors (HTSC) YBa 2 Cu 2.985 57 Fe 0.015 O 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 Mossbauer 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 Mossbauer 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 Mossbauer spectrum components is demonstrated.