Relaxor-like Behavior and Structure Features of Bi₂Ti₂O₇ Pyrochlore Single Crystals

By slow cooling of the melt, large Bi2Ti2O7 single crystals with a composition close to stoichiometric were grown. No traces of impurity phases were found on the X-ray diffraction patterns. A structural model with the space group Fd3m and displacive disorder in Bi-sublattice was proposed based on X-ray single crystal diffraction data. The dielectric properties of Bi2Ti2O7 single crystals as a function of temperature at different frequencies were studied for the first time. As in the case of ceramic samples, a step-like frequency-dependent anomaly was detected at a temperature of about 220 K at a frequency of 1 kHz. It was found that attempts to describe the dielectric relaxation using the Arrhenius equation do not lead to physically significant values of the fitting parameters. However, the relaxation behavior is well described by the empirical Vogel–Fulcher relation, which is typical for many dipole and spin glasses, as well as relaxor ferroelectrics. Based on the value of fitting parameters, Bi2Ti2O7 oc...