Effects of DC bias on dielectric and electrical responses in (Y plus Zn) co-doped CaCu3Ti4O12 perovskite oxides

The dielectric and electrical properties of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics were investigated under an applied DC bias. Crystalline structure, ceramic microstructure, electrical responses and dielectric properties were systematically investigated. The lattice parameter of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics increased with increasing Zn2+ dopant concentration. The microstructure had grain sizes of 2-4 mu m and was slightly changed with Zn2+ concentration. High dielectric permittivities (epsilon' similar to 4400-5000) and very-low loss tangents (tan delta similar to 0.03-0.06) were successfully achieved. At 1 kHz, epsilon' slightly increased with increasing Zn2+ concentration, while tan delta was significantly reduced. Variations in a low-frequency tan delta values in a low-frequency range were consistent with changes in the grain boundary resistance. Using impedance spectroscopy, it was found that the grain boundary resistance was significantly reduced by applying a DC bias, while the grain resistance remained unchanged. The conduction activation energy at the grain boundaries tended to decrease with increasing DC bias voltage (0-36 V), which was due to the reduction in the potential barrier height at the grain boundaries. The dielectric and electrical properties were described by the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.