Phase equilibria of the SrO-Yb2O3-CuOx system in air

The phase diagram for the SrO-Yb2O3-CuOx system was, investigated in air. The solid solution (Sr14-xYbx)Cu24Oz (0<x<less than or equal to>1) (the '14-24' phase) was the only ternary phase formed. This phase exhibits a smaller range of solid solution compared with similar phases containing larger lanthanide ions. Transmission electron microscopy (TEM) studies of (Sr,,Yb)Cu,,O, indicated that the phase was incommensurate, with the modulation wave vector q=(1/2-z)c*, z approximate to0.066. The Sr-analogs of the Ba2YbCu3O6+x high T-c superconductor and the associated BaYb2CuO5 'green phase' were not observed in the system. The ionic size of lanthanides 'R' in the SrO-R2O3-CuOx systems affects the number of compounds formed and their crystal chemistry. The phase diagrams exhibit a smaller number of solid-solution phases with decreasing size of R-cations, reflecting the lanthanide contraction. (C) 2001 Published by Elsevier Science Ltd.