Effect of (Ba0.6Sr0.4)TiO3 (BST) Doping on Dielectric Properties of CaCu3Ti4O12 (CCTO)

The effect of (Ba0.6Sr0.4)TiO3(BST) addition on dielectric properties of CaCu3Ti4O12 (CCTO) ceramic was investigated. Ceramic samples with the chemical formula (1-x)CaCu3Ti4O12 + x(Ba-0.6,Sr-0.4)TiO3 (x=0, 0.05, 0.1, and 0.2) were synthesized from high purity oxide powders by the conventional solid-state synthesis method. X-ray diffraction (XRD) analysis showed the existence of BST as a secondary phase alongside CCTO. Scanning electron microscopy (SEM) investigation showed a slight decrease in grain size of doped CCTO samples. Density measurements showed that porosity content increased with increasing BST addition indicating low densification due to high melting point secondary phase addition. Dielectric constant of undoped CCTO (x=0) showed lack of stability with frequency which dropped drastically between 10(4) and 10(5) Hz and accompanied by high dielectric loss. Addition of BST into CCTO caused the dielectric constant to slightly decrease but improved stability with frequency compared to the undoped sample. The decrease in dielectric constant of doped CCTO samples was suggested to be partly due to the decrease in average grain size and increase in porosity with BST addition. Nevertheless, a high value of dielectric constant was still maintained around similar to 10(4) range for all doped samples. The dielectric loss (tan delta) of all BST-doped samples was lower than that of pure CCTO sample at the frequency range of 10(3) to 10(5) Hz probably due to the increase of grains boundary resistivity. The activation energy of grains boundary (E-gb) showed higher values as compared to the activation energy of grains (E-g) for all samples and conforms to the internal barrier layer capacitor (IBLC) model.