Study on the variable color and emissivity properties of Co doped TiO2 under temperature fluctuations

In this paper, Co doped TiO2 powders were prepared through solid-state reaction. The effects of sintering temperature on microstructures, morphologies, variable color and emissivity properties of the Co doped TiO2 powders were investigated in detail. The results show that Co2+ ions substitute for Ti4+ ions effectively in rutile TiO2 after heat-treating at 900 °C-1200 °C. Increasing sintering temperature from 900 °C to 1200 °C improves crystalline quality, substitution amount of Co2+ for Ti4+ and oxygen concentration of the Co doped TiO2 powders. All the Co doped TiO2 powders show reversible thermochromism, which are green at room temperature and yellow at testing temperature of ∼800 °C. Simultaneously, the maximum variation of infrared emissivity reaches to 0.332 with testing temperature changing from room temperature to 800 °C in the powders sintered at 1100 °C. The Co doped TiO2 powders are competitive materials for smart stealth compatible visible light and infrared wavebands.