Origin of the Optical Anomalies Near the Ferroelectric Phase Transition in SbSI and SbSBr Crystals

Abstract

Experimental investigation of SbSI exponential absorption tail of slope σ/kT(T) and isoabsorption energy E ^K (T) at K = const reveal that in ferroelectric phase transition region at T _c the slope σ/kT(T) has anomalous behavior. Explanation of this phenomena presented using electronic potential V(z) dependence upon high frequency mode B_1u symmetry normal coordinates in (z) direction taking into account thermal fluctuations of the atoms in x − y plane. The splitting of B_1u normal modes in double-well V(z) explains anomalous behavior σ/kT(T) at the ferroelectric phase transition region in SbSI and SbSBr crystals.

Keywords:

• SbSI
• SbSBr
• phase transitions
• optical anomalies

Communicated by Dr. George W. Taylor