Grain-boundary and subgrain-boundary effects on the dielectric properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 ceramic samples sintered at different temperatures were studied by measurements of microstructural and dielectric properties. Electron microscopy for thermally-etched samples confirmed a microstructure with subgrains (SG) buried in a crystalline grain. The detailed dielectric properties were shown to be conformable with the double-barrier-layer capacitance model. The complex electric modulus analysis revealed unambiguously each contribution of the SG interiors, SG boundaries and grain boundaries to the dielectric constant. Our result clarified how the dielectric properties change with increasing sintering temperature. It was concluded that grain boundaries rather than SG boundaries played the key role in the low-frequency giant dielectric constant in CCTO ceramics.