Single-Oscillator Model of the “Soft-Mode” Lattice Vibration in the Perovskite-Type Ferroelectrics

Abstract

The existence of the temperature dependent “soft mode” in a perovskite-type ferroelectric crystal has been concluded from the temperature independence of the frequency ν_m, at which reflectivity assumes minimum, by using the classical dispersion relation of the single-oscillator model. The temperature dependence of the “soft-mode” frequency of several crystals has been calculated and compared with experimental results. The temperature dependence of reflectivity spectra in far-infrared and infrared regions has been computed, where a certain temperature dependence of the damping constant was taken into account. The existence of the “soft mode” in the ferroelectric phase, the over-damping effect and some other phenomena are discussed.