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

Abstract The microstructural evolution, non‐Ohmic properties, and giant dielectric properties of CaCu 3 Ti 4− x Ge x O 12 ceramics ( x =0‐0.10) are systematically investigated. The Rietveld refinement confirms the existence of a pure CaCu 3 Ti 4 O 12 phase in all samples. Significantly enlarged grain sizes of CaCu 3 Ti 4− x Ge x O 12 ceramics are associated with the liquid phase sintering mechanism. Enhanced dielectric permittivity from 6.90×10 4 to 1.08×10 5 can be achieved by increasing Ge 4+ dopant from x =0‐0.10, whereas the loss tangent is remarkably reduced by a factor of ≈10. Non ‐ Ohmic properties are enhanced by Ge 4+ 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 + /Cu 2+ and Ti 3+ /Ti 4+ ratios, which are calculated from the X‐ray absorption near‐edge structure.