Abstract
The results of ultrasonic velocity and attenuation measurements in Sn2P2S6 semiconductor crystals near the ferroelectric phase transition are presented for X, Y, Z crystalografic directions. It is shown that in ferroelectric phase for Y and Z directions the temperature dependencies can be well described by Landau theory and dispersion does not occur in the frequency range 10 MHz — 17 GHz. The strong frequency dispersion of ultrasonic velocity have been observed only in the direction of ferroelectric X axis.