Oxygen Dynamics in Transition Metal Doped Bismuth Oxides

A detailed quasielastic neutron scattering (QENS) study provides direct insights into the mechanism of ionic conduction in the Type II transition metal-doped bismuth oxides Bi22W5O48, Bi22Nb5O45.5 and Bi22W2.5Nb2.5O46.75. Quantitative analysis of the QENS broadening reveals an oscillating behavior similar to that observed recently for pure fluorite-type δ-Bi2O3, which can be adequately modeled by a coherent adaption of the Chudley-Elliot jump diffusion model. In conjunction with detailed ab initio molecular dynamics simulations, this shows that oxygen diffuses through these compounds almost exclusively within fluorite-type regions via an isotropic, liquid-like mechanism. The average oxygen jump length is slightly shorter than half the length of the fluorite-type subcell; this is attributed to the flexible coordination environments around Bi, in contrast to the more regular coordination environments around the transition metal dopants, which localize vacancies and prevent the remaining oxygen atoms from contributing to the overall oxygen diffusivity