The far-infrared emissivity and near-infrared reflectance of Mg1-xMnxFe2O4 synthesized by xerogel-microwave method

Red and brown inorganic pigments Mg1-xMnxFe2O4 (x = 0.0, 0.2, 0.3, 0.4, 0.5) with high far-infrared emissivity and high near-infrared reflectivity were synthesized by the xerogel-microwave method. The pure spinel structure of compounds was confirmed by various methods (X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), and Raman spectroscopy). From the XRD analysis, we can find that a shift in the decreased XRD angle is observed with the addition of the Mn2+ ions because of the radius differences between host ions (Mg2+) and dopant ions (Mn2+) as well as the John-Teller distortion. Furthermore, the results of XRD and Raman spectroscopy demonstrated that Mn dopants can inhibit the grain growth. Meanwhile, the reflective properties were measured by UV–vis–NIR spectrophotometer and the NIR solar reflectance values in the 1400–2500 nm range are over 66% with a maximum 82.9% (x = 0.2). In the experiment where Mn2+ replaced Mg2+ in MgFe2O4, the band gap decreased from 2.14 eV to 1.86 eV, which results in the decrease of the NIR solar reflectance in 800–1400 nm range. At last, the infrared emissivity of the samples was measured at room temperature, and the average emissivity is over 0.8 with maximum 0.85 (x = 0.5), which is due to the lattice distortion and the intensification of asymmetrical vibration of the Mn–O, Mg–O and Fe–O bonds. •Red and brown inorganic pigments Mg1-xMnxFe2O4 were synthesized by the xerogel-microwave method.•The pigments Mg1-xMnxFe2O4 possess the high far-infrared emissivity and high near-infrared reflectivity.•The pigments Mg1-xMnxFe2O4 could be candidates for “cool pigments”.