Abstract
In this work Lorenz field coefficients F for SbSI type crystals are estimated. Also transverse and longitudinal frequencies (ω T and ω l) of optical vibrations are determined. From a study of these quantities it was concluded that a combination of F is an inadequate condition for ferroelectric phase transitions to take place. Taking the electronic structure, chemical bond model, electronic potential and condition ω T—>0 into account, the phase transition in SbSI type crystals was investigated. The dependence of the electronic potential upon the composition of V-VI-VII crystals and mixed crystals has revealed the factors that change the phase transition temperature T c and the dynamics of the soft mode.
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