Soft mode and its electronic potential in SbSI-type mixed crystals

Abstract

The paper presents the results of ferroelectric dispersion at microwaves and of calculation of electronic potential dependence upon normal coordinates of B1u mode in paraelectric and ferroelectric phases in SbSI-type mixed crystals. Obtained large anharmonicity of the electronic potential at Sb (or Bi) site confirms the splitting of the soft B1a mode, the main component of which causes the ferroelectric dispersion at microwaves. Dependence of the electronic potential on composition revealed all factors which change the temperature of phase transition and the soft mode dynamics. It also explains why the pure SbSeI, BiSI and BiSel are not ferroelectrics.