Conduction mechanism and dielectric relaxation in high dielectric KxTiyNi1-x-yO

Complex impedance spectroscopic study has been made to elucidate the conductivity mechanism and dielectric relaxations in a low loss giant dielectric (epsilon(')similar to 10(4)) KxTiyNi1-x-yO (KTNO) system with x=0.05-0.30 and y=0.02 over a wide temperature range (200-400 K). Below ambient temperature (300 K), dc conductivity follows variable range hopping mechanism. The estimated activation energy for dielectric relaxation is found to be higher than the corresponding polaron hopping energy, which is attributed to the combined effect of K-doped grains and highly disordered grain boundary (GB) contributions in KTNO. Observed sharp fall of epsilon(') below similar to 270 K is ascribed to the freezing of charge carriers. Comparatively lower value of relaxation time distribution parameter beta of KTNO than that of the CaCu3Ti4O12 (CCTO) system reveals more disorder in KTNO. It is also found that KTNO is structurally more stable compared to the CCTO system, both having giant epsilon(') value.