Significantly improved giant dielectric response in giant dielectric response in CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05, 0.10) ceramics

The dielectric properties and electrical responses of an undoped CaCu3Ti4O12 ceramic and isovalent codoped CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05 and 0.10) ceramics were investigated. Significant increases in the grain size can be observed in all the CaCu2.95Ni0.05Ti4-xGexO12 ceramics. The CaCu2.95Ni0.05Ti4-xGexO12 ceramics were shown to exhibit giant dielectric properties, high dielectric permittivities similar to 4.83-4.96 x 10(4), and very low tan delta values similar to 0.029-0.030. Additionally, the ceramics all demonstrated nonlinear current density-electric field (J-E) characteristics. The significantly improved dielectric properties of the (Ni2+, Ge4+)-codoped CaCu3Ti4O12 ceramics are closely associated with the enhanced grain boundary response. Clearly, the giant dielectric properties of the CaCu3Ti4O12 and CaCu2.95Ni0.05Ti4-xGexO12 ceramics could be well described by an internal barrier layer capacitor (IBLC) mechanism, which was confirmed by the results of the impedance spectroscopy and applied DC bias analysis. The important roles of the Ni2+ and Ge4+ isovalent dopants are discussed.