Raman-Scattering Study of the Soft Phonon Modes in Hexagonal Barium Titanate

Abstract

The Raman spectrum of hexagonal BaTiO 3 has been investigated in the temperature range from 2 K to room temperature. Below the structural-phase-transition temperature of T a (∼222 K), we find the corresponding underdamped soft-phonon modes; the mode frequencies are proportional to ( T a - T ) β with β∼1/3 in a wide temperature range (0.5< T / T a <0.95). Although, in the ferroelectric phase below T c (∼74 K), several new features are observed, no soft mode which correlates with the ferroelectric transition is found.