On the problem of the LO–TO splitting of the soft mode in CaTiO$_3$

The dispersion analysis of the panorama reflection spectrum of ceramic calcium titanate has been performed following the additive and factorized dispersion models with the goal to reveal the degree of adequacy of each of these models for determining the dispersion parameters of phonon modes. The correspondence of longitudinal and transverse IR-active vibrations has been established for the cubic and orthorhombic phases. Giant LO–TO splitting of the low-frequency soft mode (700 cm$^{-1}$), which leads to the inversion of the frequencies of all other IR vibrations in this region, has been found. This result is in good agreement with first-principles calculations.