OPTICAL PROPERTIES OF Sn2P2S6 CRYSTALS.

An investigation was made of the long-wavelength infrared transmission spectra, Raman scattering spectra, photoconductivity, and edge absorption in the ferroelectric Sn//2P//2S//6 grown from the vapor phase. At T equals 295 degree K, the spontaneous polarization was 10 mu C/cm**2 and the width of the forbidden gap was E//g equals 2. 3 eV. The transparency range extended from 0. 53 to 8 mu . The observed absorption bands at 8. 1 and 9. 5 mu were attributed to two-phonon processes. The structure of one-phonon bands in the 33-600 cm** minus **1 range, governed by the P-S, Sn-S, and P-P bonds was in agreement with the characteristic features of the crystal structure of Sn//2P//2S//6.