Constructing multiple heterogeneous shell on the CaCu3Ti4O12 core for better dielectric performances

A core-shell synthesis is proposed in this study to improve the dielectric loss and the resistivity of CaCu3Ti4O12 (CCTO), which exhibits a colossal permittivity, make it very interesting for capacitor applications. However, the grain boundaries of this ceramic material play a key role for the good dielectric properties. To control these boundaries can be performed by producing shells around the CCTO grains with different oxide mixtures. The design of core-shell structure is a possible approach to control the thickness and homogeneity of the shell, which will improve the properties of this material. In this work, as-prepared CCTO particles, synthetized by solid-state reaction, were successful coated with double or triple shell (SiO2, Al2O3, TiO2) using conventional sol-gel pro-cessing derivative from Stober method. This coating with several binary oxides is made for the first time and has an innovative character in the improvement of properties for an application The CCTO coated with shell composed of SiO2 +Al2O3 +TiO2 mixture showed the best improvement with a colossal permittivity about 7.10(4), low loss tangent close to 0.05 and high resistivity equal to 10(9) Omega cm at 1 kHz. Indeed, a clear increasing of resistivity and decreasing of dielectric loss were observed for these samples compared with the resistivity of CCTO (approximate to 10(5) Omega cm). Moreover, simulations of impedance curves give the capacitance and resistivity of the grain boundaries, which confirm by their linear behavior that the global properties of this material depend on the behavior of the grain boundaries in agreement with the Internal Bayer Layer Capacitors model.

Automated summary

A core-shell synthesis method is proposed to improve the dielectric loss and resistivity of CaCu3Ti4O12 (CCTO) for capacitor applications. The grain boundaries of CCTO play a key role in its dielectric properties, and controlling these boundaries by producing shells around the CCTO grains with different oxide mixtures can improve the material's properties. In this study, CCTO particles were successfully coated with double or triple shell (SiO2, Al2O3, TiO2) using sol-gel processing. The CCTO coated with a shell composed of SiO2 + Al2O3 + TiO2 mixture showed the best improvement in terms of colossal permittivity, low loss tangent, and high resistivity.