Microstructural evolution, non-Ohmic properties, and giant dielectric response in CaCu3Ti4-xGexO12 ceramics

The microstructural evolution, non-Ohmic properties, and giant dielectric properties of CaCu3Ti4-xGexO12 ceramics (x=0-0.10) are systematically investigated. The Rietveld refinement confirms the existence of a pure CaCu3Ti4O12 phase in all samples. Significantly enlarged grain sizes of CaCu3Ti4-xGexO12 ceramics are associated with the liquid phase sintering mechanism. Enhanced dielectric permittivity from 6.909x10(4) to 1.089x10(5) can be achieved by increasing Ge4+ dopant from x=0-0.10, whereas the loss tangent is remarkably reduced by a factor of approximate to 10. Non-Ohmic properties are enhanced by Ge4+ doping ions. Using impedance and admittance spectroscopies, the underlying mechanisms for the dielectric and nonlinear properties are well described. The improved nonlinear properties and reduced loss tangent are attributed to the enhanced resistance and conduction activation energy of the grain boundaries. The largely enhanced permittivity is closely associated with the enlarged grain sizes and the increase in the Cu+/Cu2+ and Ti3+/Ti4+ ratios, which are calculated from the X-ray absorption near-edge structure.