Determination of the normal vibrational displacements in several perovskites by inelastic neutron scattering

Relative displacements of the atoms corresponding to the lowest frequency long wavelength transverse optic phonon of several materials with the perovskite structure were determined directly by a least-squares refinement of the integrated intensity of inelastic neutron scattering. The modes of KTaO3 and SrTiO3 were identified as being of the Slater type, in which oxygen atoms vibrate against Ta and Ti atoms. In the case of RbMnF3, however, an entirely different vibrational motion was obtained, in which Rb ions vibrate out of phase with the rigid MnF3 group.