Temperature and compositional behaviour of electrical conductivity and optical absorption edge in Cu7Ge(S1 − xSex)5I mixed superionic crystals

Electrical and optical properties of Cu7Ge(S1 − xSex)5I mixed crystals, grown by chemical vapour transport, are studied. Compositional dependencies of their electrical conductivity, measured in the frequency range 1.0 ⋅ 106–1.2 ⋅ 109 Hz at 100–300 K and the corresponding activation energy, are analysed. The optical absorption edge of Cu7Ge(S1 − xSex)5I mixed crystals is studied in the temperature range 77–300 K, the compositional dependencies of the optical pseudogap and Urbach energy being obtained. The effect of different types of disordering on the optical absorption processes at S → Se anionic substitution in the Cu7Ge(S1 − xSex)5I mixed crystals is investigated.