Strongly Enhanced Dielectric Response and Structural Investigation of (Sr2+, Ge4+) Co-Doped CCTO Ceramics

A solid–state reaction method was used to prepare (Sr2+, Ge4+) co-doped CaCu3Ti4O12 ceramics. A single-phase of CaCu3Ti4O12 was detected in all the ceramics. An enormous evolution of grain growth in (Sr2+, Ge4+) co-doped CaCu3Ti4O12 ceramics was observed, which was due to a liquid phase sintering mechanism. Theoretical calculations showed that Ge dopant ions are more likely substituted in Cu sites rather than Ti sites. High dielectric permittivity, ∼69,889, with a low dielectric loss tangent, ∼0.038, was achieved in a Ca0.95Sr0.05Cu3Ti3.95Ge0.05O12 ceramic. Furthermore, dielectric permittivity at 1 kHz of this ceramic is more temperature-stable than that of the CaCu3Ti4O12 and Ca0.95Sr0.05Cu3Ti4O12 ceramics. The enhanced dielectric permittivity with reduced loss tangent in the co-doped ceramics originated from a metastable insulating phase created by a liquid phase sintering mechanism. The local insulating phase along the grain boundary layers can increase the grain boundary resistance as well as the conduction activation energy of the grain boundaries, resulting in a decreased dielectric loss tangent. An internal barrier layer capacitor model supports the origin of the giant dielectric properties in CaCu3Ti4O12-based ceramics by all results in this work.