The Influence of Microstructure and Emissivity of NiO-Doped Fe3O4 Spinel Structure on Near- and Middle-Infrared Radiation

The ferrites of spinel structure have high-infrared emissivity performance at high temperature, which make it possible to be used in metallurgical industry. Based on the preparation of the materials, microstructure and ions distribution of spinel structure Fe3O4 with Ni-ion doping was investigated. Further, the emissivity was measured as 0.97 in the 3–5 μm waveband at 500 °C, which presented excellent radiation performance. The first-principle calculation was conducted to explain the mechanism of emissivity variation with Ni-ion doping. The calculation results show that Ni doping makes the forbidden band increase, leading to a decrease of free carrier absorption in NiFe2O4 system, and this indicates that the Ni2+ doping would enhance the energy of electron transition from valence band to conduction band which is formed due to the hybridization of the 3d orbital electrons of the Ni ions and the 2p orbital electrons of the oxygen atoms.