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

Enhanced dielectric response and non-Ohmic properties of Ge-doped CaTiO3/CaCu3Ti4O12

We present a method for increasing the dielectric constant of CaTiO3/CaCu3Ti4O12 (CTO/CCTO) composites and retaining a low-loss tangent (tanδ) by doping with Ge dopant. The Ge-doped CTO/CCTO composites were fabricated using a one-step processing method. The phase composition and microstructure analyses confirmed the existence of CTO and CCTO phases, in which Ge doping ions can be substituted into both phases. The mean grain sizes of the two phases were slightly reduced by decreasing the porosity. Doping the CTO/CCTO with Ge doping ions resulted in a high dielectric constant by ~ two times, while a very low tanδ value of ~0.01 did not change. Furthermore, the dielectric constant changed by less than ±15% in the temperature range of −60 – 150°C. The nonlinear current density–electric field properties of CTO/CCTO can also be enhanced. Impedance spectroscopy showed a heterogeneous microstructure with enhanced grain boundary properties after doping with Ge dopants, giving rise to enhanced nonlinear electrical properties. The decreased grain resistivity due to Ge substitution is confirmed to originate from the increase in the Ti3+/Ti4+ ratio, which was analyzed using X–ray photoelectron spectroscopy