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

Ultrasonic and piezoelectric studies of two-dimensional layered crystalline structures of (MMP2X6)-P-1 (M,M-1 = 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 T-c approximate to 312 K in CuInP2S6; two successive phase transitions at T-c1 approximate to 180 K and T-c2 approximate to 145 K in CuCrP2S6; and two phase transitions at T-c1 approximate to 235 K and T-c2 approximate to 228 K in CuInP2Se6. (c) 2005 Elsevier Ltd. All rights reserved.