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

The effect of La^sup 3+^ doping on Ca^sup 2+^ sites in CaCu^sub 3^Ti^sub 4^O^sub 12^ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca^sub (1-x)^La^sub (2/3)x^Cu^sub 3^Ti^sub 4^O^sub 12^ 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 La^sup 3+^ doping. The dielectric and impedance characteristics of Ca^sub (1-x)^La^sub (2/3)x^Cu^sub 3^Ti^sub 4^O^sub 12^ 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 La^sup 3+^ substitution. The dielectric constant of CaCu^sub 3^Ti^sub 4^O^sub 12^ decreased drastically on La^sup 3+^ doping. The frequency and temperature responses of dielectric constant of La^sup 3+^ doped samples were found to be similar to that of CaCu^sub 3^Ti^sub 4^O^sub 12^. The effects of La^sup 3+^ doping on the electrical properties of CaCu^sub 3^Ti^sub 4^O^sub 12^ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La^sup 3+^ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La^sup 3+^ doped CCTO ceramics were unambiguously established by modulus spectra studies.[PUBLICATION ABSTRACT]