Leading role of grain boundaries in colossal permittivity of doped and undoped CCTO

The role of grain boundaries in the colossal permittivity ɛ of doped and undoped calcium copper titanate, CaCu3Ti4O12 (CCTO), is illustrated by a first correlation – over four orders of magnitude – between ɛ and the capacity of grain boundaries, not that of grains, deduced from the analysis of impedance measurements. The DC resistance of the CCTO sample which is essential to make efficient capacitors for technological applications, as well as the loss factor tan(δ), are found to be correlated with the resistance of the grain boundaries rather than that of the grains. The correlation extends over almost seven orders of magnitude. These findings, consistent with the internal barrier layer capacitance (IBLC) model, indicate the leading role of grain boundaries in the origin of the capacitance of CCTO samples.