Electron microscopic investigations of the as-synthesised and dissociated Y: 124 HTSC phases

Abstract

The Y: 124 was synthesised at ambient oxygen pressure using an oxygen enhancer (NaNO3). The as-synthesised material was thermally dissociated at 915°C for various time spans, e.g., 1, 2 and 5 min. X-ray diffraction (XRD) results showed that the undissociated sample corresponds to the Y: 124 phase, whereas the dissociated samples consisted of mixed phases. For the samples dissociated for 1 min these were Y: 124 and Y: 123 (with some traces of CuO), for dissociation times of 2 and 5 min these were dominantly Y: 123 and CuO. From R-T and L-T (inductance-temperature) measurements, it was found that the undissociated Y: 124 possesses a Tc(R=0) ≈80 K and there is no drop in inductance for dissociated samples (2 and 5 min). Microstructural investigations of Y: 124 revealed that the material dissociated for 1 min is biphasic, consisting of Y: 124 and Y: 123. Besides stacking disorder, local area superstructures along "c" emanating from the native Y: 124 phase were also observed. This is thought to ensue from the random and sequential removal of CuO chains from the Y: 124 structure. The sample subjected to longer dissociation times, i.e., 2 and 5 min consists of Y: 123 and CuO precipitates. For longer dissociation times, e.g. 2 min and above. the Y: 124 phase nearly completely converts into Y: 123 and CuO. © 1992.