Vibrational Spectra of Some Crystals Having Near-Perovskite Structure

Abstract

Studies of the transmission and reflection spectra of the perovskite crystals SrTiO₃, BaTiO₃, and CaTiO₃ over a wide frequency range have shown that the observed vibrational spectra of their crystal lattices agree with those predicted by the theory of symmetry. But neither the theory nor the experimental results provide the form of the normal modes. The only exceptions are the F_2u (O_h) vibration ?₁ and the corresponding B₁ (C_4v) vibration, whose form is given by symmetry alone. The form of the normal modes for the perovskite lattice is, nevertheless, a very important problem. The knowledge of their form is of intrinsic interest and is also useful in connection with estimation of various microscopic properties of BaTiO3, discussed in Chapter VI.