Instability of the Order–Disorder Ferroelectrics

抄録

An instability of the order–disorder ferroelectrics is studied in the variationl method at finite temperature. A double-well potential based on the unfied oscillator model is adopted as a trial potential and a crystal potential is given by superposing the back-to-back Morse potentials. It is shown that occurrence of the instability is attributed to changes in shape of the crystal potential. The transition temperature and the soft mode frequency are shown in terms of the microscopic quantities dependent on substances.