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

We report on the studies for temperature dependences of elastic stiffness coefficients in Sn2P2S6 crystals. Basing on the construction of acoustic velocity surfaces, we have determined the parameters of the slowest acoustic wave that propagates in Sn2P2S6 crystals. The acoustooptic figure of merit for the case of acoustooptic interaction with this wave is estimated as ∼0.8 × 10−12 s3/kg. We have shown that Sn2P2S6 is very close to the conditions of tricritical point on the (x, T)- and (p, T)-phase diagrams of the solid solutions Sn2P2(SexS1−x)6. The critical exponent α of the heat capacity for the Sn2P2S6 crystals is equal to 0.42 ± 0.03.

► We have constructed the acoustic velocity surfaces.
► We have determined the direction of the slowest acoustic wave.
► We have calculated acousto-optic figure of merit for the slowest acoustic wave.
► We have shown that the Sn2P2S6 crystals are very close to the tricritical point.
► We have calculate the value of critical exponent for the Sn2P2S6 crystals.