Microstructure and dielectric properties of CaCu3Ti4O12 ceramics by quenching after sintering in low vacuum and thermobaric treatment at 9 GPa

Abstract

Calcium copper titanium oxide (CaCu3Ti4O12, CCTO) ceramics were quenched in air and liquid nitrogen separately after being subjected to sintering in low vacuum and thermobaric treatment (TBT) at 9 GPa and 1000 °C for 10 min. The refined XRD patterns showed cubic body-centered perovskite-related structure of CaCu3Ti4O12. TBT and quenching caused extra low-intensity peaks of TiO2 and Cu. The grain size decreased significantly from ~ 100 µm to ~ 30 µm and the configuration of grain boundary became indistinguishable after the post-treatment. The big grain size contributed to the large dielectric constant of low vacuum-sintered CCTO. Two semicircles in the complex impedance spectra (Z* plots) can be observed in the temperature range of 291–450 K that corresponding to contributions of grain boundary and grain. An apparent decreasing of the large arc diameter at low frequency suggested a reduction of the grain boundary resistance Rgb by TBT, which should be related with the conduction phase of Cu. The smaller difference between Rgb and Rg (grain resistance) led to weaker interfacial polarization and then smaller dielectric constant of TBT-treated CCTO ceramics than the low vacuum-sintered ones.