Impedance spectroscopy of Bi3.25La0.75Ti3O12 ceramics above and below ferroelectric transition temperatures

摘要

The complex impedance of Bi3.25La0.75Ti3O12 ceramic was measured over a temperature range 50-600 degrees C at several frequencies. The complex capacitance anomaly of the ferroelectric phase transitions was observed near T-c = 395 degrees C. Remarkable capacitance dispersion of the complex capacitance was found above 250 degrees C. The complex impedance spectra above 250 degrees 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 similar to 0.33 eV above Tc and E similar to 0.44 eV below Tc in the high-frequency regions, and E similar to 0.32 eV above T-c and E similar to 0.57 eV below Tc in the low-frequency regions.