Dielectric relaxation in Bi2Ti2O7 single crystals

Large impurity-free Bi2Ti2O7 single crystals were grown by slow cooling of a melt. Their crystal structure and dielectric properties as a function of temperature at different frequencies were studied for the first time. A step-like frequency-dependent anomaly was observed at a temperature of about 220 K at a frequency of 1 kHz. The relaxation behavior is well described by the empirical Vogel-Fulcher relation typical for relaxor ferroelectrics. Based on the value of fitting parameters, Bi2Ti2O7 occupies an intermediate position between the canonical relaxor PbMg1/3Nb2/3O3 on the one hand and lead-free relaxors based on BaTiO3 on the other hand. The possible mechanisms of the observed dielectric relaxation of the Bi2Ti2O7 single crystals are discussed.