Temperature behavior of absorption edge of CuCr0.3In0.7P2S6 layered crystals


Purpose. After authors of [1, 2] have shown that CuInP2S6 and CuСrP2S6 crystals can be used as a next generation, energy independent memory storage and different vdW heterostructures - we can observe a significant growth of interest in these crustals. Besides, they are interesting objects for experimental investigations because they show different types of dipole order and you can observe fero-, feri-, antifero-, incommensurate and dipole glass state on the phase diagrams of these crystals.
Methods. Studied CuCr0.3In0.7P2S6 crystals were grown by the gas transport reaction method. For the measurements we have been using samples of 40-80 mkm size. Temperature of the sample has been controlled by an cuprumconstantan thermocouple with an accuracy of 0,1 K. The absorption spectrum has been investigated using an «Ocean optics» USB 400 spectrometer with an 190-1000 nm wave length recording range.
Results. Spectral dependencies of the absorption coefficient of the CuCr0.3In0.7P2S6 Ccrytals have been investigated for different temperatures. It has been determined that in the investigated temeratures range the absorption edge has exponential form. Based on the investigations of the absorption edge the temperature behavior of the energy positioning of the absorption edge of the CuCr0.3In0.7P2S6 crystals has been established. The absorption edge energy jump is related to the phase transition in this crystals occurs at the temperature T = 222 K.
Conclusions. Optical absorption spectrums of CuCr0.3In0.7P2S6 crystals in the temperature ranges of 150-350 K have been investigated. It has been found that theabsorption edge has an exponential nature and obeys the Urbach rule. All the main parameters of the Urbach law have been determined. First order phase transition of CuCr0.3In0.7P2S6 crystals occurs at the temperature Tc = 222 К

Keywords: ferroelectrics, phase transitions, absorption spectra