Controlling microstructure and significantly increased dielectric permittivity with largely reduced dielectric loss in CaCu3−xGexTi4O12 ceramics

Microstructure, dielectric, and electrical properties of CaCu3−xGexTi4O12 ceramics with x = 0–0.10 prepared by a conventional solid-state reaction method are investigated. Single-phase of CaCu3Ti4O12 was detected in all sintered ceramics. The substitution of Ge4+ into Cu2+ sites results in the grain size of CaCu3−xGexTi4O12 ceramics to decrease, compared to CaCu3Ti4O12 ceramic. Unusually, although grain sizes of CaCu3−xGexTi4O12 ceramics decrease, their dielectric permittivity is increased by doping. Enhanced dielectric permittivity ~ 35,000–42,000 with reduced loss tangent ~ 0.037–0.053 was achieved in x = 0.025–0.10. Improved dielectric properties with reduced loss tangent might be originated by enhanced grain boundary response, especially the largely increased grain boundary resistance. The result obtained from an impedance spectroscopy technique indicates the formation of an internal barrier layer capacitor model in all sintered ceramics. The giant dielectric permittivity of CaCu3−xGexTi4O12 ceramics might be caused by intrinsically compensating mechanisms of charge carriers.