Relaxation of Li-dipole pairs in the disordered perovskite K1-xLixTaO3 andthe effect of external electric fields

It has been well established by several studies that the relaxer perovskite K1-xLixTaO3 (KLT) exhibits two distinct relaxation modes in its dielectric spectrum, with respective barrier heights about 1200 and 2400 K. While the mode with the smaller barrier (known as pi /2 relaxation) is responsible f or the complex relaxer behavior of KLT, the relaxation connected with the l arger barrier involves pairs of lithium dipoles reorienting as a single uni t (known as pi relaxation). A detailed study of this relaxation over a broa d temperature range for nominal lithium concentrations 3.5% to 16% is prese nted here. The measured dielectric dispersion and absorption for all concen trations over this temperature range is shown to be in agreement with the C ole-Cole modification of the complex Debye dielectric response. Implicit in this modification is the recognition of a distribution of relaxation times in terms of two parameters alpha and tau (m). We find that the parameter a lpha connected with the distribution function, increases with increasing co ncentration and decreasing temperature. Furthermore, alpha also decreases i n presence of a de bias field. In addition, the bias field reduces the diel ectric loss and hardens the relaxation frequency. The distribution of relax ation times and its temperature evolution are explained in terms the random static electric fields due to frozen Li-dipole pairs.