Influence of compositional disorder on optical absorption processes in Cu₆P(S_1−xSe_x)₅I crystals

The fundamental absorption edge of Cu₆P(S_0.6Se_0.4)₅I and Cu₆P(S_0.4Se_0.6)₅I crystals was studied in the 77–320 K temperature range where no phase transitions were revealed by optical techniques. The temperature behavior of the exponential Urbach absorption edge in Cu₆P(S_0.6Se_0.4)₅I and Cu₆P(S_0.4Se_0.6)₅I crystals was analyzed. The effect of compositional disorder upon the Urbach edge parameters, parameters of exciton-phonon interaction, and lattice parameters in Cu₆P(S_1−xSe_x)₅I, 0 ≤ x ≤ 1, crystals was studied. The effect of various types of disordering upon the optical absorption processes in Cu₆P(S_1−xSe_x)₅I crystals is discussed.