Oblique Phonons with Special Concern to the Soft Phonon in Tetragonal BaTiO₃

Abstract

Raman spectra of oblique phonons in a tetragonal BaTiO₃ single crystal were obtained for different angle θ which the phonon wavevector q makes with the c-axis. A complete analysis of the data has been made on the basis of Merten’s equation. The spectrum of the oblique phonon on the branch that runs from the overdamped soft E(x)TO phonon to the underdamped 175 cm⁻¹ A₁(z)TO phonon has been found to show a peak in the range θ\gtrsim30°. This result provides a new method of obtaining the temperature dependence of the overdamped soft phonon.