Giant LO-TO Frequency Splitting of the Soft Mode in Perovskites

The dispersion analysis of the dielectric spectra of the perovskite ceramics, CaTiO3, and perovskite-like monocrystalline thin films (Ba,Sr)TiO3 deposited on a monocrystalline MgO substrate is carried out. The giant LO–TO splitting (∼700 cm−1) of the lowest-frequency absorption band (the soft mode) is found. Due to that splitting the LO and TO frequencies of other phonons are inverted. The result is in a good agreement with first-principle calculations.