Temperature behaviour of fundamental absorption edge in superionic Ag6PS5I crystals

. Ag 6 PS 5 I single crystals are grown from solution–melt by means of a vertical zone crystallization method. Dispersion of the refractive index of Ag 6 PS 5 I measured with a spectral ellipsometry technique is described by a known Wemple– DiDomenico relation. The fundamental absorption edge for the Ag 6 PS 5 I 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 Ag 6 PS 5 I is studied.