Mechanism of copper doping in cerium(IV) oxidepowder and its effect on 3–5 μm infrared emissivity

In this study, Ce1−xCuxO2−x (x = 0, 0.01, 0.03, 0.05, 0.07) samples were prepared by hydrothermal method. The structure, microstructure, and elemental composition of the powders were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, whereas the electrical conductivity, ultraviolet–visible absorption spectroscopy, and infrared emissivity at 3–5 μm were measured as well. Moreover, the effects of Cu2+ doping concentration on the microstructure, morphology, bandgap, conductivity, and infrared emissivity of Cu-doped CeO2 powders were systematically studied. The effects of Cu2+ doping on infrared reflection and absorption in a 3–5 μm band and their mechanisms were explained based on electromagnetic theory, lattice vibration absorption, and free carrier absorption. Our result indicated that the emissivity of 1% Cu-doped powder reached the lowest emissivity of 0.200 at 800 °C. When the doping concentration was above 1%, the curve of infrared emissivity versus temperature exhibited a “U” shape, with the minimum point shifting towards the low-temperature region with the increase of Cu doping amount. This phenomenon was attributed to the different enhancement amplitude of reflectivity and absorbance of CeO2 powder by Cu2+ at different temperatures.