DIELECTRIC AND ELASTIC PROPERTIES OF FERROELECTRIC MATERIALS AT ELEVATED-TEMPERATURE

The temperature dependence of the velocities of sound propagating alon g various directions in high quality mono-domain single crystals of Ba TiO3 and PbTiO3 have been measured by Brillouin scattering. Using the velocities and dielectric permittivities measured by the impedance met hod, the elastic stiffness moduli, C-ijkl, piezoelectric constants, e( rij) and dielectric permittivity, epsilon(ij), have been determined at elevated temperature through the ferroelectric phase transition. Only the longitudinal compressive modulus along the polar c-axis of tetrag onal PbTiO3 exhibits a distinctive soft mode behavior. In BaTiO3 the e lectromechanical properties are found to be significantly different at different frequencies. It is suggested that high frequency relaxation occurs in BaTiO3.