Influence of Processing Conditions on the Electrical Properties of CaCu 3 Ti 4 O 12 Ceramics

The electrical properties of a series of CaCu 3 Ti 4 O 12 ceramics prepared by the mixed oxide route and sintered at 1115°C in air for 1–24 h to produce different ceramic microstructures have been studied by Impedance Spectroscopy. As‐fired ceramics are electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries, and can be modelled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The grain boundary resistance and capacitance values vary as a function of sintering time and correlate with the ceramic microstructure based on the brickwork layer model for electroceramics. The large range of apparent high permittivity values for CaCu 3 Ti 4 O 12 ceramics is therefore attributed to variations in ceramic microstructure. The grain‐boundary resistance decreases by three to four orders of magnitude after heat treatment in N 2 at 800°–1000°C but can be recovered to the original value by heat treatment in O 2 at 1000°C. The bulk resistivity decreases from ∼80 to 30 Ω·cm with increasing sintering time but is independent of heat treatment in N 2 or O 2 at 800°–1000°C. The origin of the bulk semiconductivity is discussed and appears to be related to partial decomposition of CaCu 3 Ti 4 O 12 at the high sintering temperatures required to form dense ceramics, and not to oxygen loss.