Innovative non-thermal plasma coating for “core–shell” CaCu3Ti4O12 material

Abstract

Colossal permittivity of CaCu3Ti4O12 (CCTO) makes it a very interesting candidate for capacitor applications. To improve its properties, an innovative physical method based on a pulsed non-thermal micro-plasma treatment was set up to realize the coating of CCTO's grains (core) with silicon oxide (shell). This method is adapted to control the thickness and homogeneity of the shell, which will allow a better control of grain–grain boundary interfaces and improve the properties of this material. Best result is obtained for the set of gas mixture: Ar/O2/hexamethyldisiloxane (HMDSO) = 2028 N cm3 min−1/7.84 N cm3 min−1/523 mg h−1, respectively, in plasma with a shell thickness of 50 nm. This study offers a new opportunity to quickly synthetize core–shell materials with a dry technique and without almost no secondary product resulting from the chemical reaction because it is in the gaseous state. A complete analysis of the plasma by optical emission spectroscopy in the UV-visible range shows that HMDSO molecules are totally dissociated in atomic (Si, C, and O) or simple radical species (C2 and CH) in the plasma phase. In addition, several thermometer species (OH°, CH, CN, N2, and N2+) are used to estimate excitation temperatures of the plasma (Trot, Tvib, and Te = 300 K, 2400–3700 K, and 5.3 eV, respectively) that clearly shows the non-equilibrium character and the efficiency of this plasma.