Preparation, infrared emissivity and thermochromic properties of Co doped ZnO by solid state reaction

In this paper, green Zn1-xCoxO nanopowders were synthesized via solid-state reaction at different calcination temperatures. The effects of sinterring temperature on structure, morphologies, color and infrared emissivity was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-visible absorption spectroscopy, Raman spectroscopy and IR-2 dual-band infrared emissometer, respectively. The results show that the as-synthesized samples have hexagonal wurtzite structure and meantime the peaks of the secondary phase, Co3O4, were observed when the sinterring temperature is below 900 °C. The sintering temperature plays a vital important role in crystallite sizes, lattice parameters, volume of the unit cell as well as microstructure. According to the EDS results, Zn ions were substituted by the Co ions in the ZnO lattice where Co ions present in the +2 state indicated via XPS analysis. Additionally, UV-visible absorption spectra shows that absorption edge have a red shift while the corresponding energy band gap of the semiconductor nanoparticles decrease with the increasing sintering temperature, which affects the thermochromic characteristics of materials significantly. The infrared emissivity is related to the microstructure, grain size, conductivity and lattice vibration.