Improved giant dielectric properties of CaCu3Ti4O12via 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 δ < 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 ≈10⁴ to ≈10⁵. 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.