Infrared Transmission Spectrum and Lattice Vibration Analysis of Some Perovskite Fluorides

Abstract

Infrared absorption spectra of the perovskite fluorides KMF3(M:Ni, Mg, and Zn) and NaNiF3 have been measured in the region 700 to 50 cm−1 at room temperature and liquid‐nitrogen temperature. Three absorption bands for KMF3 were observed and these have been assigned to the f 1u lattice modes. A normal‐coordinate analysis of the crystal as a whole has been performed and the interatomic force constants in the crystal have been obtained. The forms of the normal modes of the lattice vibrations have been fully described on the basis of the normal‐coordinate treatment. Vibrational assignments have been supported from the experimental ground (temperature effect) and the theoretical side. The compound NaNiF3 reveals a much more complicated spectrum than those of KMF3, which suggests a structure of an appreciable deformation from the regular cubic perovskite. The analysis of the lattice vibrations for the rutile counterparts has been made based on the normal‐coordinate treatment by the use of the force constants transferred from the corresponding perovskite. The result gives another evidence for the lattice vibration assignments of the perovskite fluorides.