Effects of structure and electronic properties of spinel ferrites on their emissivity in middle and short wavebands

Abstract In this study, the samples of a series of spinel ferrites (Fe3O4, NiFe2O4, and CuFe2O4) were prepared to investigate their emissivity performance in the middle and short wavebands. The emissivity of the samples was measured in the temperature range of 27–500 °C. The results show that Fe3O4 had the highest average emissivity values of 0.98 in 8–14 μm waveband and 0.97 in 3–5 μm waveband. In addition, CuFe2O4 had the second-highest values of 0.95 in 8–14 μm waveband and 0.92 in 3–5 μm waveband. Finally, NiFe2O4 had the lowest values of 0.94 in 8–14 μm waveband and 0.59 in 3–5 μm waveband. Given that the force constant KO has an effect on the lattice distortion, which, in turn, is an important factor influencing the emissivity performance in 8–14 μm waveband, infrared spectrum measurements and an X-ray diffraction refinement of the spinel ferrites were performed for the calculation of KO. The results show that Fe3O4 had a smaller KO value (94.64 × 10 3 ) than NiFe2O4 (95.37 × 10 3 ) and CuFe2O4 (94.72 × 10 3 ), which confirms that KO has an inverse relationship with the emissivity in 8–14 μm waveband for the studied series of spinel ferrites. Furthermore, the first-principles calculation was used to discuss the effect of electronic transition on the emissivity in 3–5 μm waveband. The calculation results show that, for Fe3O4, the O 2p orbitals pass through the Fermi level, resulting in the electronic transition near the Fermi level needs less energy to overcome the band gap than that for NiFe2O4 and CuFe2O4, which indicates that the electronic transition for Fe3O4 is easier. This implies that Fe3O4 would have higher emissivity in 3–5 μm waveband than NiFe2O4 and CuFe2O4 do. The band gap values of the series of spinel ferrite samples were measured by UV–Vis diffuse reflectance spectroscopy, and the variation trend of the band gap values is opposite to that of the 3–5 μm band emissivity. This study implies that the development of high-infrared-radiation materials with a ferrite spinel structure should aim at reducing the force constant KO and band gap, which is a possible direction for future research.