ANOMALOUS DIELECTRIC-RELAXATION IN LITHIUM-POTASSIUM TANTALATE CRYSTALS

In order to describe the unusual dielectric properties observed in K1-xLixTaO3 crystals a ne- approach is proposed. The dynamical Glauber theory, previously applied to spin-glasses, is modified by the introduction of the spectral distribution of the random interactions between the dipoles associated with the Li+ ions. Moreover, the dipole correlations are taken into account by the Onsager reaction field. As a result, the calculated dielectric constant reproduces well the unusual features of the Argand diagrams and, in particular, their finite slope at low frequencies and infinite slope at high frequencies (strophoidal shape). The temperature dependence of some parameters shows, however, the limits of a spin-glass type model in describing the collective behaviour of randomly distributed dipoles in a highly polarizable medium.