Ultrasonic and piezoelectric studies of new layered ferroelectric compounds of Sn2P2S6 family

Ultrasonic and piezoelectric studies of two-dimensional layered crystalline structures of MM1P2X6 (M,M1 = Cu, In, Sn, Cr; X = S, Se) are presented in this contribution. It was shown, that such materials: CuInP2S6, CuCrP2S6 and CuInP2Se6 undergo phase transitions (PT) and exhibit piezoelectric effect in low temperature phases. Anomalies of ultrasonic velocity and attenuation at phase transitions have been observed in these materials. Measurements of temperature dependencies of ultrasonic velocity and attenuation revealed the first order phase transition at Tc ≈ 312 K in CuInP2S6; two successive phase transitions at Tc1 ≈ 180 K and Tc2 ≈ 145 K in CuCrP2S6; and two phase transitions at Tc1 ≈ 235 K and Tc2 ≈ 228 K in CuInP2Se6.