Influences of Sr2+ Doping on Microstructure, Giant Dielectric Behavior, and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites

The microstructure, dielectric response, and nonlinear current-voltage properties of Sr2+-doped CaCu3Ti4O12/CaTiO3 (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr2+ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr2+ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr2+, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr2+-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces

Giant dielectric behavior and non-ohmic properties in Mg2++F− co-doped CaCu3Ti4O12 ceramics

A solid–state reaction method was used to produce CaCu3-xMgxTi4O12-2xF2x with x values of 0, 0.05, and 0.10. A CaCu3Ti4O12 phase was detected in the absence of impurities. The (Mg2++F–) co–doping ions inhibited the grain growth of the CaCu3Ti4O12 ceramics because of the solute drag mechanism. The dielectric and non–Ohmic electrical properties of the CaCu3-xMgxTi4O12-2xF2x ceramics were studied. Intriguingly, the ceramic with x = 0.05 enhanced the dielectric properties with a considerably decreased loss tangent (tanδ~0.06) while retaining a high dielectric permittivity (>104) at 1 kHz. The nonlinear current density–electric field (J–E) properties of the ceramic with x = 0.05 were also successfully improved. However, the dielectric and nonlinear properties deteriorated when x = 0.10. The variations in the low–frequency tanδ and electric breakdown strength were primarily associated with the grain size and Schottky barrier height at the grain boundaries. The relevant mechanisms for these improved dielectric and non–Ohmic properties are discussed based on the effect of the internal barrier layer capacitor

Improved giant dielectric properties of CaCu₃Ti₄O₁₂via simultaneously tuning the electrical properties of grains and grain boundaries by F⁻ substitution

A novel concept to simultaneously modify the electric responses of the grain and grain boundaries of CaCu3Ti4O12 ceramics was proposed, involving doping with F− anions to improve the giant dielectric properties