Abstract
For pt.I see ibid., vol.9, p.1571 (1976). The general group-theoretical method of discussing the frequency and strength changes in infrared and Raman spectra due to Landau-type structural phase transitions derived previously, is applied to 18 types of the best known structural phase transitions in dielectric crystals: SrTiO3, LaAlO3, SiO2, NH4Cl, NH4Br, NaNO3, BaMnF4, (CH3NH3)2MnCl4, DyVO4, NaN3, KH2PO4, BaTiO3, LiTaO3, SbSI, NaNO2, (NH4)2SO4, Gd2(MoO4)3, and RbH3(SeO3)2. The frequency splitting is in the lowest order in all cases proportional to eta s or eta s2, where eta s is the spontaneous value of the order parameter. The infrared or Raman strength of modes which become active in the distorted phase is in the lowest order proportional to delta s2, or delta s4. The available experimental data are discussed and in most cases a good agreement with theory is found.