Dipole glassy state evidence for CuInP2(SexS1-x)6 ferrielectric mixed crystals from Raman scattering and optical absorption data

The temperature and concentration dependences of Raman scattering and optical absorption spectra for CuInP2(SexS1-x)6 crystals are investigated. Similarly to dynamic disordering of Cu+ ions at the transition from ferrielectric into paraelectric phase for CuInP2S6 compound, static disordering of these ions in the mixed crystals in the dipole glassy state at low temperatures determines rise in the phonon damping and increase in the energetic width w of exponential optical absorption edge. The concentration and temperature dependences w(T,x) clearly reveal “asymmetry” of the dipole ordering on T–x phase diagram: the dipole glassy state smoothly evolves into ferrielectric one, coexisting with the latter under decrease of selenium content till x = 0. The dipole glassy state sharply transforms into ferrielectric phase with growing selenium concentration, passing through the relaxor state in the region of x = 0.7–0.8.