Enhanced dielectric response and non-Ohmic properties of Cd-doped Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics

In this study, Na-1/3(Ca1-xCdx)(1/3)Bi1/3Cu3Ti4O12 (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 40-10(6) Hz. Moreover, improvement in non-Ohmic properties was also observed with Cd2+ doping. The optimal dielectric properties (dielectric constant of similar to 12,500, dielectric loss of similar to 0.032 at 10 kHz, nonlinear coefficient of similar to 3.42, and breakdown strength of similar to 2.7 kV<middle dot>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 degrees C-220 degrees 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.