Improved giant dielectric properties of CaCu3Ti4O12 via simultaneously tuning the electrical properties of grains and grain boundaries by F- substitution

Abstract

A novel concept to simultaneously modify the electric responses of the grain and grain boundaries of CaCu3Ti4O12 ceramics was proposed, involving doping with F- anions to improve the giant dielectric properties. The grain growth rate of CaCu3Ti4O12 ceramics was enhanced by doping with F- anions, which were found to be homogeneously dispersed in the microstructure. Substitution of F- anions can cause an increase in the resistance of the insulating grain boundary and a decrease in the grain resistance. The former originated from the ability of the F- dopant to enhance the Schottky barrier height at the grain boundaries, leading to a great decrease in the dielectric loss tangent by a factor of 5 (tan delta < 0.1). The latter was primarily attributed to the increase in Ti3+ and Cu+ concentrations due to charge compensation, resulting in a significantly enhanced intensity of space charge polarization at the grain boundaries. This is the primary cause of the increase in dielectric permittivity from approximate to 10(4) to approximate to 10(5). The giant dielectric and electrical properties were well described by the Maxwell-Wagner polarization relaxation based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.