Synthesis of CCTO powder for application in humidity sensor

Abstract

Materials with high dielectric constants are indispensable for miniaturized electronic devices. Electro-ceramic materials such as CCTO, BaTiO3 have been synthesized and studied by a number of researchers, during recent decades, for various applications. Among them, CCTO deserves special attention due to its giant dielectric behavior that leads to its applications in gas and humidity sensors, antennas, resistive switches, etc. In this study, CCTO powder was synthesized by an environment-friendly, low-cost chemical method using egg-white solution of Ca(NO3)2, Cu(NO3)2 and titanium (diisopropoxide) bis-(2,4-pentanedionate). The decomposition and crystallization temperature of the above product was determined by Thermogravimetric Analysis (TGA) and Differential Thermal Annealing (DTA). The powder was calcined at 700-800 °C for 8 h in a muffle furnace for single-phase crystallization. The structure and optical properties of the CCTO powder were investigated by X-rays diffraction and diffuse reflectance spectroscopy (DRS). The DRS study revealed the semiconductor like behavior of CCTO powder showing a bandgap like transition in the visible region (2.1-2.2 eV). Capacitive type humidity sensor devices were fabricated using CCTO pellets sintered at 1100 °C. Change in the capacitances of the above devices with a change in the relative humidity of the atmosphere was systematically investigated at various frequencies. An enhanced rate of change of the capacitance with respect to the relative humidity as observed in all our devices invites a promising application in high-efficiency humidity sensors.