Influence of Dislocations in CdS Crystal on Its Electromechanical Coupling Factors

The electromechanical coupling factors are measured in the frequency range from 100 kHz to 260 MHz for CdS single crystals with various dislocation densities. These measurements show that each of the electromechanical coupling factors kt, k15, and k31 begins to decrease in a steep slope as the density of dislocation which terminates at c surface of the crystal exceeds an amount around 106 cm−2. However, these coupling factors come back toward the normal values when the density of dislocation is decreased by means of the annealing of the crystals in a sulfur vapor. No appreciable change of the elastic constants and the dielectric constants is observed. Therefore, the observed variation of the electromechanical coupling factors is attributable to the dependence of the corresponding piezoelectric constants on the dislocation density.