Ferroelectric phase transition in SbSI type crystals

In this work Lorenz field coefficients F for SbSI type crystals are estimat ed. Also transverse and longitudinal frequencies (omega(T) and omega(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 ferroelec tric phase transitions to take place. Taking the electronic structure, chem ical bond model, electronic potential and condition omega(T)-->0 into accou nt, the phase transition in SbSI type crystals was investigated. The depend ence of the electronic potential upon the composition of V-VI-VII crystals and mixed crystals has revealed the factors that change the phase transitio n temperature Te and the dynamics of the soft mode.