Enhancement of dielectric response by the interaction of point defect and grain boundary in copper tantalate oxides

As particular cubic perovskite-type materials, copper tantalate Cu2Ta4O12 (CTO) displays a giant-dielectric phenomenon. A thermal-treatment method for enhancing the dielectric response of CTO is developed. The air-quenching Cu2Ta4O12 (CTOq) and slowing-furnace-cooling Cu2Ta4O12 (CTOs) were fabricated and identified with cubic crystal structure. The CTOs sample shows a colossal permittivity (104 - 107) in a broad frequency (40 Hz–105 Hz) and temperature region (300 K–470 K). The permittivity dependence of frequency for CTOq and CTOs samples were described by the Maxwell-Wagner relaxation and Cole-Cole relation. The low-frequency dielectric response associates with the internal barrier layer capacitor effect intensified by oxygen vacancies, while in the high-frequency range it is mainly involved in the relaxation induced by charged point defects in grains. The concentration of the point defects was evidenced by XPS with Cu+, Cu2+ and oxygen. The impedance, electrical modulus and conductivity behavior of the samples at selected temperature were also described. The results indicate that the colossal permittivity response is related to interaction mechanism of point defects and grain boundaries, which can be modified by the thermal treatment process.