Bundit Putasaeng

The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be describe...

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

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 (tanδ < 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.

Effects of La3+ doping ions on dielectric properties and formation of Schottky barriers at internal interfaces in a Ca2Cu2Ti4O12 composite system

Abstract Influences of La3+ substitution on the dielectric properties and formation of Schottky barriers at internal interfaces of a Ca2Cu2Ti4O12 (CaTiO3/CaCu3Ti4O12) composite system were investigated. It was found that electrostatic potential barrier height was greatly reduced by doping with La3+, leading to a large decrease in the total resistance of internal interfaces between grains. This observation was attributed to the creation of conduction electrons, which were possibly induced by electrical charge compensation of La3+ substitution into Ca2+ sites. Variations in the dielectric properties of La3+-doped CaTiO3/CaCu3Ti4O12 composite ceramics and nonlinear properties can be described based on the electrical responses at the internal interfaces between CaCu3Ti4O12–CaCu3Ti4O12 grains and CaTiO3–CaCu3Ti4O12 grains. Influence of possible charge compensation due to different levels of La3+ dopant on the formation of potential barriers was discussed.