Infrared absorption spectra of the perovskite fluorides KMF3(M:Ni, Mg, and Zn) and NaNiF3have been measured in the region 700 to 50 cmminus;1at room temperature and liquidhyphen;nitrogen temperature. Three absorption bands for KMF3were observed and these have been assigned to thef1ulattice modes. A normalhyphen;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 normalhyphen;coordinate treatment. Vibrational assignments have been supported from the experimental ground (temperature effect) and the theoretical side. The compound NaNiF3reveals 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 normalhyphen;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.
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