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

We have measured in a K1-xLixTaO3 crystal with x = 1.7 % the elastic c onstant with longitudinal acoustic waves of frequency between 30 and 3 30 MHz and the dielectric constant between 10 Hz and 1 MHz in the temp erature range from 4 to 200 K under an electric field applied upon coo ling. 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 wa s also studied. These results are explained by the occurrence of clust ers of oriented dipoles borne by the Li+ ions, favoured by the field.