Coupling of Li+ relaxators to the soft mode in KTaO3 : Li

The complex dielectric permittivity of K1-xLixTaO3 (KTL) single crystals wi th x = 0.006 has been experimentally studied in detail in the temperature i nterval from 5 to 300 K and at frequencies from 100 Hz to 1 MHz. In agreeme nt with previous studies, a very large effect of the Li impurities on the d ielectric response, even for such a small Li concentration, is found. It co nsists in the appearance of a pronounced low-temperature dielectric dispers ion with giant magnitude. This unusually large dielectric response cannot b e caused only by the relaxation of the Li+-impurity off-centres themselves, because the Li concentration is too small. Also, the host lattice response itself cannot give such a large dispersion, as evidenced. We present a the oretical model, which considers the coupling of the Li+-related relaxators to the TO soft mode, giving a good description of the experimental data obt ained.