Effect of Nickel and Cobalt co-substitution on the structural and dielectric properties of Barium Titanate ceramics

The influence of Nickel and Cobalt co-substitution on the structure and dielectric properties of barium titanate (BaTiO₃) ceramics has been investigated. Nickel and Cobalt co-substituted BaTiO₃ ceramics with general formula BaTi_1−x(Ni,Co)_xO₃ has been synthesized for x = 0.0, 0.02, 0.04 and 0.08 through conventional solid state reaction route. The structural analysis carried out by X-ray diffraction reveals the successful incorporation of Ni²⁺ and Co²⁺ ions in the Ti⁴⁺ site of BaTiO₃ with all samples under study having tetragonal structure. However the tetragonality (c/a ratio) seems to be decreasing with increase of co-substitution. The dielectric measurements are done at different frequencies and temperatures. The room temperature dielectric constant decreased considerably for the Ni and Co co-substituted samples. The phase transition of the BaTi_1−x(Ni,Co)_xO₃ has been investigated by studying the temperature dependence of dielectric constant. Nickel and Cobalt co-substituted samples showed diffused nature of phase transition with a notable reduction in the Curie temperature with the increase of co-substitution. The Curie temperature is reduced to 104 °C for x = 0.08 composition whereas for x = 0.0 the Curie temperature is 123 °C. Enhancement in conductivity is observed with addition of Nickel and Cobalt addition. Nearest-neighbour hopping model is used to explain the conduction in the samples under study and energy of activation for conduction is calculated from Arrhenius plot.