Constant-wavelength neutron diffraction study of cubic perovskites BaTaO₂N and BaNbO₂N

Abstract

Local structural disorder of perovskite oxynitrides BaTaO₂N and BaNbO₂N is investigated by constant-wavelength neutron powder diffraction measurements at 300 and 6 K. Temperature-dependent diffraction line-broadening analyses together with the Rietveld refinements confirm that both perovskites retain average structures of simple cubic symmetry down to 6 K. While the Ta and Nb atoms in the above oxynitrides have remarkably large displacement parameters, indicative of pronounced octahedral distortions, the rigidity of Ba sublattice seems to suppress the cooperative propagation of long-range octahedral tilting.