Colossal dielectric response in erbium iron garnet ceramics

Polycrystalline Er3Fe5O12 ceramic sample was synthesized by a solid-state reaction technique. The dielectric properties of the sample were experimentally studied. A colossal dielectric constant more than 10(3) was observed over a wide temperature and frequency range. The dielectric relaxation in the sample was identified by the measurement of permittivity modulus, impedance spectroscopy, and conductivity in detail. At relatively low temperatures (T < 600 K), the dielectric relaxation under high frequencies (f >= 50 kHz) is triggered by the dipolar effect accompanied by the Fe2+ and Fe3+ charge transitions, while that under low frequencies (f <= 50 kHz) is mainly be associated with the Maxwell-Wagner effect. Moreover, a low-frequency dielectric relaxation at high temperatures (T >= 600 K) is probably evolving from the contribution of oxygen vacancies and grain boundaries, which is also suggested to be the origin of the colossal dielectric constant.