Elastic and acoustooptic properties of Sn2P2S6 crystals: Effect of ferroelectric phase transition

Abstract We report on the studies for temperature dependences of elastic stiffness coefficients in Sn 2 P 2 S 6 crystals. Basing on the construction of acoustic velocity surfaces, we have determined the parameters of the slowest acoustic wave that propagates in Sn 2 P 2 S 6 crystals. The acoustooptic figure of merit for the case of acoustooptic interaction with this wave is estimated as ∼0.8 × 10 −12 s 3 /kg. We have shown that Sn 2 P 2 S 6 is very close to the conditions of tricritical point on the ( x , T )- and ( p , T )-phase diagrams of the solid solutions Sn 2 P 2 (Se x S 1− x ) 6 . The critical exponent α of the heat capacity for the Sn 2 P 2 S 6 crystals is equal to 0.42 ± 0.03.