Total scattering analysis of cation coordination and vacancy pair distribution in Yb substituted delta-Bi2O3

Reverse Monte Carlo (RMC) modelling of neutron total scattering data, combined with conventional Rietveld analysis of x-ray and neutron data, has been used to describe the cation coordination environments and vacancy pair distribution in the oxide ion conducting electrolyte Bi3YbO6. The thermal variation of the cubic fluorite unit cell volume, monitored by variable temperature x-ray and neutron experiments, reveals significant curvature, which is explained by changes in the oxide ion distribution. There is a significant increase in tetrahedral oxide ion vacancy concentration relative to delta-Bi2O3, due to the creation of Frenkel defects associated with the Yb3+ cation. The tetrahedral oxide ion vacancy concentration increases from room temperature to 800 degrees C, but little change is observed in the vacancy pair distribution with temperature. The vacancy pair distributions at both temperatures are consistent with a favouring of vacancy pairs