Ceramics of CaCu3-xCoxTi4O12 (CCCTO, x ¼ 0, 0.2, 0.4 and 0.6), with cubic lattice structure, were fabricated using a semi-wet method. The dielectric properties of the prepared samples were studied at 1 kHz frequency in the temperature range of 300e600 K, as well as in the frequency range of 50 Hze200 kHz at room temperature. The results showed that the dielectric constants of the as-prepared samples in the frequency range of 50 Hze200 kHz, at room temperature, are reasonably high (1.7  104  ε  6  104). It was also found out that the dielectric loss (tand) of the prepared samples decreased by increasing the cobalt concentration at low and middle frequencies. The dielectric loss decreased from 0.87 for an undoped sample CaCu3Ti4O12 (CCTO), to 0.15 for a doped sample (CCCTO) with x ¼ 0.6, at 50 Hz frequency. However, the dielectric constant (ε) values for the samples doped with cobalt were found to be higher than that of for the undoped sample. Moreover, the XRD patterns as well as the SEM images and EDX results revealed that the Cu-rich phase (CuO) decreased at the CCTO grain boundaries, while at the same time Co2TiO4 and CaTiO3 phases with good dielectric insulating behavior having been formed at the boundaries. This causes the increase of the resistance at the grain boundaries leading to lower leakage current which in turn results in a decrease of the dielectric loss. These results were confirmed by using the impedance spectroscopy analysis. Our results indicate that the cobalt doped CCTO ceramics can be suggested as good candidates to be used in fabricating microelectronic and memory devices with high dielectric constant and low dielectric loss

Keywords