Relationship between crystal structure and oxide-ion conduction in Nd2Zr2O7 and La2Zr2O7 deduced by high-temperature neutron diffraction

Crystal structures of Nd2Zr2O7 were refined by the Rietveld analysis of neutron diffraction data at 1098, 1217, 1348 and 1467 K, while those of La2Zr2O7 were refined at 1070, 1188, 1306 and 1435 K. Nd2Zr2O7 had the pyrochlore-type structure with the oxygen vacancy distributed over all oxide-ion sites between 1098 and 1467 K. On the other hand, La2Zr2O7 had the pyrochlore-type structure with almost complete ordering for oxygen vacancy up to 1070 K. The change in oxide-ion conductivity (σ) in Nd2Zr2O7 and La2Zr2O7 can be related to a change in the product of site occupancy (g48f) and the oxygen vacancy rate (1-g48f) in the O3 (48f) site, g48f(1-g48f).