EFFECT OF THE ELECTRIC-FIELD ON THE ELASTIC AND DIELECTRIC-PROPERTIES OF A LITHIUM-POTASSIUM TANTALATE CRYSTAL

We have measured in a K1-xLixTaO3 crystal with x = 1.7 % the elastic constant with longitudinal acoustic waves of frequency between 30 and 330 MHz and the dielectric constant between 10 Hz and 1 MHz in the temperature range from 4 to 200 K under an electric field applied upon cooling. The main effect of the applied field on the dielectric constant is attributed to space charges. The real part of the elastic constant (the sound velocity) was found to increase when the field was applied perpendicular to the acoustic wave vector and to decrease when it was applied parallel to the wave vector. The effect of the cooling rate was also studied. These results are explained by the occurrence of clusters of oriented dipoles borne by the Li+ ions, favoured by the field.