Local Disorder in Proton Conductor BaSn_0.5In_0.5O_2.75 Analyzed by Neutron Diffraction/ Atomic Pair Distribution Function

Abstract

We carried out the neutron powder diffraction study to reveal the local disorder in the proton conductor BaSn_0.5In_0.5O_2.75. We analyzed this material by the combination of the Rietveld refinement and the maximum entropy method and confirmed that this material has the cubic structure with the space group of Pm3m, and that Sn and In atoms randomly occupy 1b site. However, the atomic pair distribution function (PDF) indicated that this material can be fitted well by the structural model with a tetragonal phase, P4/mmm from the original-cubic structure below the maximum distance between a pair of atoms, r_max of 6 Å, and as r_max increases, this disorder is released and that structure changes to the original-cubic structure. We found that the local structural disorder is caused by the displacement of Ba and O atoms.