Effect of reduction produced defects on the dielectric relaxation and electrical conduction of Na0.5Bi0.5TiO3-based ceramics

Abstract

The chemical reduction has often been exploited to improve the dielectric, piezoelectric, and flexoelectric response of the perovskite oxides. In this work, the effect of reduction on the dielectric properties of Na0.5Bi0.5TiO3-based ceramics was investigated in a broad temperature range from −130 to 175 °C. After the reduction of the ceramics, three dielectric anomalies were observed. The two dielectric anomalies at a low temperature exhibit a thermally activated dielectric relaxation characteristic with an activation energy of ∼0.3 eV. Evidence indicates that the two dielectric anomalies are related to the hopping of electrons between the defective lattice sites which has an interaction with the dipoles existing in the bulk and the region close to the ceramic surface, respectively. The third dielectric anomaly is observed around room temperature, and the frequency-independent dielectric constant and loss are greatly increased in the reduced ceramics. The origin of the dielectric anomaly is argued to be related to the interaction of water with the ceramic surface region. The reduction produces a large number of oxygen vacancies, facilitating the water adsorption on the surface of the reduced ceramics. The interaction greatly increases the migration and conduction of protons, generating a pronounced dielectric anomaly. We also show that the similar dielectric anomaly, though very weak, also appears in other unreduced perovskite-type oxides, indicating that the interaction of water with the surface is a common phenomenon in perovskite-type oxides.