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 6K. Temperature-dependent diffraction line-broadening analyses together with the Rietveld refinements confirm that both perovskites retain average structures of simple cubic symmetry down to 6K.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. © 2011 The Ceramic Society of Japan.