Enhanced giant dielectric properties and improved nonlinear electrical response in acceptor-donor (Al^(3+), Ta^(5+))-substituted CaCu_(3)Ti_(4)0_(12) ceramics

The giant dielectric bchavior of CaCu_(3)Ti_(4)0_(12)(CCTO)has been widely investigated owing to its potential applications in electronics;however,the loss tangent(tan8)of this material is too large for many applications.A partial substitution of CCTO ceramics with either Al^(3+) or Ta^(5+)-ions generally results in poorer nonlinear properties and an associated increase in tan8(to~0.29-1.15).However,first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Tit 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 tan8(~0.010--0.036)were obtained by simultaneous partial substitution of CCTO with acceptor-donor(Al^(3+),Ta^(5+))dopants to produce(Al^(3+),Ta^(5+))-CCTO ceramics.The reduced tan8 and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure.The signifcant reduction in the mean grain size of the(Al^(3+),Ta^(5+))-CCTO ceramics compared to pure CCTO was mainly because of the Ta^(5+)-ions.Accordingly,the increased GB density due to the reduced grain size and the larger Schottky barrier height(Ф_(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 tan8 values compared to pure and single-doped CCTO.In addition,high dielectric constant values(ε'≈(0.52-2.7)×10^(4))were obtained.A fine-grained microstructure with highly insulating GBs was obtained by Ta doping,while co-doping with Ta^(5+) and Al^(3+ )resulted in a high Ф_(b).The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.