Enhanced giant dielectric properties and improved nonlinear electrical response in acceptor-donor (Al3+, Ta5+)-substituted CaCu3Ti4O12 ceramics

The giant dielectric behavior of CaCu3Ti4O12 (CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tan delta) 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 tan delta (to similar 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 (similar to 200-6588 V/cm) and nonlinear coefficient (similar to 4.8-15.2) with a significantly reduced tan delta (similar to 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 tan delta and 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 (phi(b)) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tan delta values compared to pure and single-doped CCTO. In addition, high dielectric constant values (epsilon ' approximate to (0.52-2.7) x 10(4)) 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 phi(b). The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.

Automated summary

In this study, greatly enhanced breakdown electric field and nonlinear coefficient with reduced tan delta were achieved by simultaneous partial substitution of CCTO with acceptor-donor (Al3+, Ta5+) dopants to produce (Al3+, Ta5+)-CCTO ceramics. The improved electrical properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure, leading to enhanced grain boundary resistance. These results provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.