Disordering effect on optical absorption processes in CuInP2S6 layered ferrielectrics

The optical absorption edge of CuInP2S6 crystals is studied between 77 and 573 K. The nature of optical transitions, resulting in absorption edge formation in ferrielectric and paraelectric phases, is elucidated. The temperature variation of the energy gap in the ferrielectric phase transition range and the temperature behavior of the Urbach absorption edge in the paraelectric phase are studied. The effect of temperature and structural disordering on the absorption edge energy position and shape is analyzed.