Perspective on dielectric properties of calcium copper titanate ceramics

Abstract

Calcium Copper Titanium Oxide (CCTO) Ceramics of composition CaCu3Ti4O12 has emerged as a lead-free ceramic supercapacitor with a large dielectric constant of 104–105 at room temperature. The CCTO microstructure is electrically heterogeneous composed of semiconducting grains and insulating grain boundaries. The origin of the large dielectric constant has therefore been widely attributed to barrier layer capacitance originated at grain boundaries. Our research is focused on understanding the stability and reproducibility of the measured electrical and dielectric properties when they are used as capacitor dielectrics because of the inconsistent results obtained when tested in ambient conditions. The origin of this inconsistency is investigated through the roles of testing atmosphere, sample thickness and doping with alumina on the stability and reproducibility of dielectric properties of CCTO. The solid state reaction method is used to fabricate phase pure and dense samples. AC impedance spectroscopy is used to study the roles of testing atmospheres, temperatures, microstructures, grain boundaries, sample thickness, alumina doping and frequency on the dielectric properties. It is shown that this approach of characterizing fundamental electrical properties of CCTO can be used to eliminate hysteresis to produce stable and reproducible dielectric properties. These perspectives are presented and discussed.