On the Urbach rule in SbSI ferroelectric crystal

Abstract

Optical absorption edge of SbSI ferroelectric crystal is studied in a broad temperature range. An Urbach behaviour of the absorption edge is observed in paraelectric (T>Tc) and partly in ferroelectric (130 K <130 K. The influence of crystal lattice disordering of various types on the Urbach absorption edge parameters is studied. The non-Urbach behaviour of the absorption edge is explained by a presence of dynamic structural disordering due to temperature-dependent phonon-defect interactions.