Exceptional dielectric and varistor properties of Sr, Zn and Sn co-doped calcium copper titanate ceramics.

Calcium copper titanate (CCTO) powders associated with the chemical formula Ca 1- x Sr x Cu 3- y Zn y Ti 4- z Sn z O 12 (where x , y , z varying from 0 to 0.1) were synthesized via a solid-state reaction route. Dense ceramics (>96% of theoretical density) were obtained by sintering these powders comprising micrometer-sized grains at appropriate temperatures. X-ray powder diffraction studies confirmed the formation of monophasic CCTO cubic phase, with no traceable secondary phases present. The lattice parameter ' a ' was found to increase on increasing the dopant concentration. The microstructural studies performed on these ceramics confirmed a decrease in mean grain size (18 μm to 5 μm) with the increase in Sr, Zn and Sn doping concentrations as compared to that of undoped CCTO ceramics though they were sintered at the same temperature and duration (1100 °C/15 h). The dielectric studies (dielectric constant ( ε ') and the dielectric loss ( D )) conducted in a wide frequency range (10 2 -10 7 Hz) demonstrated an increase in ε ' and a decrease in D on increasing the doping concentration. Impedance analysis (Nyquist plots) performed on these ceramics revealed a significant increase in grain boundary resistance. The highest value of grain boundary resistance (6.05 × 10 8 Ω) (in fact this value was 100 times higher than that of pure CCTO) was obtained for the composition corresponding to x = y = z = 0.075 and intriguingly the ceramic pertaining to this composition exhibited enhanced ε ' (1.7 × 10 4 ) and lower D (0.024) at 1 kHz. Further, these co-doped CCTO ceramics exhibited substantial improvement in breakdown voltages and nonlinear coefficients ( α ). The temperature independent (30 -210 °C) dielectric response of these samples qualifies them to be suitable dielectric materials for the fabrication of multilayer ceramic chip capacitors.