Influence of grain boundary insulation on nonlinear and dielectric discrepancy in Ni2+/Ni3+ doped CaCu3-xNixTi4O12 ceramics

Abstract

Two series of CaCu3-xNixTi4O12 (x = 0.0, 0.5, 1.0, 2.5) ceramics doped with Ni2+ and Ni3+ were prepared via the solid-state reaction method. Despite the similar micro-morphologies of the samples, the nonlinear electrical characteristics were enhanced in the Ni3+-doped samples but deteriorated in their Ni2+-doped counterparts. With Ni content increasing, the breakdown field and nonlinear coefficient of Ni3+-doped samples enhanced from 0.54 to 6.14 kV cm−1 and 2.68 to 4.92 respectively while dropped from 0.98 to 0.21 kV cm−1 and 3.48 to 1.03 for Ni2+-doped samples. Impedance spectroscopy analysis revealed significant discrepancies in terms of grain boundaries between the two series of samples, which resulted in their different dielectric properties. The oxygen loss owing to the in situ formation of NiTiO3 was considered to be the crucial factor impeding grain boundary insulation, which was key to the potential barrier formation. In contrast with that of the Ni2+-doped samples, the oxygen loss of the Ni3+-doped samples was compensated by the reduction of Ni3+ to Ni2+. This helped maintain a high potential barrier height and resulted in different nonlinear characteristics of the two series.