Internal and external relaxations in ZnNb2O6 ceramics

ZnNb2O6 ceramics were prepared via conventional solid-state reaction route. The dielectric properties of ZnNb2O6 were investigated in the temperature range from room temperature (RT) to 700 °C and frequency range of 103 − 2 × 106 Hz. Our results revealed that the sample exhibits an intrinsic dielectric response with a dielectric constant of ∼20.9 below 150 °C followed by two thermally activated relaxations (R1 and R2) at higher temperatures. Both R1 and R2 are related to oxygen vacancies inherent in the sample. At temperatures higher than ∼550 °C, an external relaxation (R3) induced by dc bias was observed. By means of the dielectric permittivity, electric modulus, impedance and admittance, R1 was attributed to be a dipole-type relaxation due to the hoping motions of oxygen vacancies. R2 and R3 were ascribed to be a Maxwell-Wagner-type relaxation resulting from the space charge due to the hoping vacancies blocked by grain boundaries and electrodes, respectively.