Temperature behaviour of fundamental absorption edge in superionic Ag₆PS₅I crystals

Ag6PS5I single crystals are grown from solution-melt by means of a vertical zone crystallization method. Dispersion of the refractive index of Ag6PS5I measured with a spectral ellipsometry technique is described by a known Wemple- DiDomenico relation. The fundamental absorption edge for the Ag6PS5I crystals is studied in the temperature range 77-300 K. The temperature dependences of the optical pseudogap and the Urbach energy are analyzed in the framework of Einstein model. The parameters of electron-phonon interaction, which results in the Urbach behaviour of the fundamental absorption edge, are determined. The influence of temperature and structural disorderings on the optical absorption in Ag6PS5I is studied.