Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

Abstract

The effect of La3+ doping on Ca2+ sites in CaCu3Ti4O12 (CCTO) was examined. Polycrystalline samples in the chemical formula Ca(1-x)La(2/3)x Cu3Ti4O12 with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La3+ doping. The dielectric and impedance characteristics of Ca(1-x)La(2/3)x Cu3Ti4O12 were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La3+ substitution. The dielectric constant of CaCu3Ti4O12 decreased drastically on La3+ doping. The frequency and temperature responses of dielectric constant of La3+ doped samples were found to be similar to that of CaCu3Ti4O12. The effects of La3+ doping on the electrical properties of CaCu3Ti4O12 were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La3+ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La3+ doped CCTO ceramics were unambiguously established by modulus spectra studies.