Dielectric relaxation in Li-doped KTaO3 studied by kinetic Monte Carlo

The dielectric properties of Li-doped KTaO3 are studied by kinetic Monte Carlo, using a microscopic model derived from first-principles calculations. The method allows equilibrium and nonequilibrium simulations on very large time scales inaccessible by a molecular dynamics simulation and adequately reproduces most of the peculiar characteristics of the system: dielectric relaxation, evolving with increasing Li content of the temperature dependence of the dielectric permittivity (from single to double peaked). The real and imaginary parts of the latter are computed as a function of temperature and frequencies of the external probing electric field (from approximate to 8 kHz to approximate to 80 MHz) at three Li concentrations (0.9%, 3.0%, and 5.8%). The first-neighbor pairs of Li are evidenced to lead to the double-peaked permittivity as Li concentration increases. Our approach opens a way to an efficient simulation of relaxor ferroelectrics on mesoscopic time scales, while keeping basic ingredients derived from atomic-scale simulations.