Phonons and oxygen diffusion in BiOand (BiY)O.

We report investigation of phonons and oxygen diffusion in BiOand (BiY)O. The phonon spectra have been measured in BiOat high temperatures up to 1083 K using inelastic neutron scattering.calculations have been used to compute the individual contributions of the constituent atoms in BiOand (BiY)Oto the total phonon density of states. Our computed results indicate that as temperature is increased, there is a complete loss of sharp peak structure in the vibrational density of states.molecular dynamics simulations show that even at 1000 K in δ-phase BiO, Bi-Bi correlations remain ordered in the crystalline lattice while the correlations between O-O show liquid like disordered behavior. In the case of (BiY)O, the O-O correlations broadened at around 500 K indicating that oxygen conductivity is possible at such low temperatures in (BiY)Oalthough the conductivity is much less than that observed in the undoped high temperature δ-phase of BiO. This result is consistent with the calculated diffusion coefficients of oxygen and observation by quasielastic neutron scattering experiments. Ourmolecular dynamics calculations predict that macroscopic diffusion is attainable in (BiY)Oat much lower temperatures, which is more suited for technological applications. Our studies elucidate the easy directions of diffusion in δ-BiOand (BiY)O.