Origin of Ferroelectric Phase Transitions of BixSb1-xSI Mixed Crystals

Abstract

The nature of normal modes’ anharmonism of SbSI—type crystals is investigated in this work. In order to explain the nature of anharmonism we apply the normal vibration mode's average potential energy's dependence on amplitudes of normal coordinates along c (z)—axis. It is proved that the variation of potential barrier between two wells of double-well potential energy Vp(z) is caused by temperature T, quasihidrostatic pressure p, and mixture x. The temperature dependence of ferroelectric phase transition on quasihidrostatic pressure p and mixture x is determined for SbSI and BixSb1-xSI crystals. Applying the equality is theoretically proved that there is no ferroelectric phase transition in BixSb1-xSI crystals where x > 0.7. The ferroelectric phase transition in SbSI—type crystals and BixSb1-xSI crystals is caused by the phonon interaction's dependence on temperature, pressure and mixture.