Local and average atomic order of ion-conducting Bi0.775La0.225O1.5 studied by neutron scattering and reverse Monte Carlo simulations

Bi0.775La0.225O1.5 has been investigated by means of neutron scattering in combination with Rietveld refinement and reverse Monte Carlo (RMC) simulations to study the average and local atomic order of the material. At low temperature the crystallographic analysis shows a clear split of anionic positions similar to that reported for Sr doped bismuth oxides. Although this split appears to be absent in the average structure at high temperature, an even larger split of Bi-O local distances is found in the pair distribution function calculated from the RMC models. This latter feature can be indicative of a tendency to have similar oxygen environments for all Bi atoms at high temperature, as a precursor of the fluorite structure that is the stable phase at even higher temperatures.