Oxygen disorder and conductivity in pyrochlore and perovskite-based compounds

This paper briefly describes the results of recent high temperature powder neutron diffraction and impedance spectroscopy studies of the pyrochlore structured Zr2Nd2O7 and Zr2Gd2O7, brownmillerite structured Ba2In2O5 and perovskite structured Ba(InxZr1-x)O2.5+x/2. The ionic conductivity of Zr2Nd2O7 is found to be slightly higher that that of the more widely studied Zr2Gd2O7 compound over the temperature range similar to 500K to similar to 1300K. However, no evidence of increasing occupancy of the empty 8(b) anion sites is observed on increasing temperature and the structure distorts away from its parent fluorite arrangement. Ba2In2O5 is found to undergo an similar to 10x increase in ionic conductivity over the narrow temperature range from similar to 1140K to similar to 1230K, in broad agreement with previous studies. This transition corresponds to a change from the brownmillerite structure to a cubic perovskite arrangement with disordered anions. Ba(In1-xZrx)O2.5+x/2 Samples with x=0.1 to x=0.9 were found to adopt the cubic perovskite structure, with the lattice parameter decreasing with x.