Structural and dielectric properties of A- and B-sites doped CaCu3Ti4O12 ceramics

Abstract

The effect of doping the A site (Ca) with La and B site (Ti) with Nb, on the grain formation, crystallographic structure, electrical properties and dielectric behaviour of CaCu3Ti4O12 is investigated over wide ranges of temperature (27–150°C) and frequency (50Hz to 5MHz). Microstructure investigation of the cast compound, Ca(1−3x)La2xCu3Ti(4−5x)Nb4xO12 (x=0, 0.02 and 0.04), using Scanning Electron Microscopy (SEM) showed that co-doping would result in grain growth inhibition. Rietveld refinement of the powder diffraction data confirmed a cubic, single phase structure with space group Im3. The steady increase in the lattice volume with increasing dopant concentration confirms the incorporation of the bigger dopant molecules in the lattice. Dielectric studies using HIOKI 3552-50 LCR Hi-Tester show that the room temperature dielectric constant would considerably increase due to co-doping. Impedance spectroscopic studies reveal that the compound is electrically heterogeneous, with semi conductive grain interior and insulating grain boundaries. Doping resulted in a decrease in grain boundary resistance and consequent increase in dielectric loss at low frequency. The dielectric behaviour of compound is explained on the basis of the Internal Barrier Layer Capacitance (IBLC) model.