Enhanced dielectric response and non-Ohmic properties of Cd-doped Na_1/3Ca_1/3Bi_1/3Cu₃Ti₄O₁₂ ceramics

Abstract

In this study, Na1/3(Ca1−xCdx)1/3Bi1/3Cu3Ti4O12 (x = 0, 0.2, 0.4, 0.8, and 1.0) ceramics were prepared via solid-state method. Effects of substitution of Ca2+ with Cd2+ on the microstructure, dielectric response, and non-Ohmic properties of Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics were studied systematically. Results showed that all samples possessed single perovskite phase, in which grain size increased with the increase in Cd2+ doping content. Energy band gaps and activation energy first increased and then decreased, achieving their maxima (4.22 and 0.642 eV, respectively) at x = 0.2. Besides, dielectric constant of doped samples increased with the decrease in dielectric loss in frequency range of 40–106 Hz. Moreover, improvement in non-Ohmic properties was also observed with Cd2+ doping. The optimal dielectric properties (dielectric constant of ∼12,500, dielectric loss of ∼0.032 at 10 kHz, nonlinear coefficient of ∼3.42, and breakdown strength of ∼2.7 kV·cm−1) were achieved at x = 0.2. Dielectric response mechanism of ceramics followed internal barrier layer capacitor model while nonlinear ohmic properties were derived from Schottky barrier structure. Dielectric relaxation peaks at high temperatures (120 °C–220 °C) were associated with grain boundaries. Therefore, partial substitution of Ca2+ with Cd2+ can improve simultaneously dielectric and non-Ohmic properties of Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics, which is conducive to their application in high-energy-density storage capacitors and varistors.