Local atomic ordering in BaTaO²N studied by neutron pair distribution function analysis and density functional theory

The local structure and oxygen/nitrogen ordering of the high permittivity perovskite BaTaO₂N has been studied using a combination of neutron total scattering and density functional electronic structure calculations. Although the average structure as revealed by neutron diffraction Rietveld analysis is cubic Pm3̄m with no evidence of O/N ordering, the local structure as revealed by pair distribution function analysis of the total neutron scattering appears to favor a cis configuration of the TaO ₄N₂ polyhedra with small Ta displacements toward the N atoms. Density functional calculations similarly suggest that the cis TaO ₄N₂ polyhedron is more stable than the corresponding trans variant.