Enhanced giant dielectric properties and improved nonlinear electrical response in acceptor-donor (Al3+, Ta5+)-substituted CaCu3Ti4O12ceramics

The giant dielectric behavior of CaCu3Ti4O12(CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tanδ) of this material is too large for many applications. A partial substitution of CCTO ceramics with either Al3+or Ta5+ions generally results in poorer nonlinear properties and an associated increase in tanδ(to ~0.29–1.15). However, first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Ti4+sites, which can improve the electrical properties of the grain boundary (GB). Surprisingly, in this study, a greatly enhanced breakdown electric field (~200–6588 V/cm) and nonlinear coefficient (~4.8–15.2) with a significantly reduced tanδ(~0.010–0.036) were obtained by simultaneous partial substitution of CCTO with acceptor-donor (Al3+, Ta5+) dopants to produce (Al3+, Ta5+)-CCTO ceramics. The reduced tanδand improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure. The significant reduction in the mean grain size of the (Al3+, Ta5+)-CCTO ceramics compared to pure CCTO was mainly because of the Ta5+ions. Accordingly, the increased GB density due to the reduced grain size and the larger Schottky barrier height (Φb) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tanδvalues compared to pure and single-doped CCTO. In addition, high dielectric constant values (ε′ ≈ (0.52–2.7) × 104) were obtained. A fine-grained microstructure with highly insulating GBs was obtained by Ta5+doping, while co-doping with Ta5+and Al3+resulted in a high Φb. The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.