Impedance spectroscopy of Bi3.25La0.75Ti3O12ceramics above and below ferroelectric transition temperatures

The complex impedance of Bi3.25La0.75Ti3O12 ceramic was measured over a temperature range 50–600 °C at several frequencies. The complex capacitance anomaly of the ferroelectric phase transitions was observed near Tc = 395 °C. Remarkable capacitance dispersion of the complex capacitance was found above 250 °C. The complex impedance spectra above 250 °C were fitted by the superposition of two Cole–Cole types of relaxations. The fast component in the higher frequency region may be due to the orientational grain–grain boundary, and the slow component in the lower frequency region is interpreted as the formation and migration of ions at the surface or electrode/crystal interfacial polarization. We found two different conduction mechanisms that have different activation energies: E ~ 0.33 eV above Tc and E ~ 0.44 eV below Tc in the high-frequency regions, and E ~ 0.32 eV above Tc and E ~ 0.57 eV below Tc in the low-frequency regions.