Influence of structure on infrared emissivity of lanthanum manganites

The lanthanum manganites La1−xSrxMnO3 (0.1≤x≤0.3) were prepared by standard solid-state reaction and sol–gel method, respectively. The structure, magnetization curves, infrared absorption and infrared normal emissivity (εN) in the 3–5 and 8–14 μm wavebands of the samples were systematically investigated. The samples prepared by solid-state reaction are rhombohedral, and the samples obtained by sol–gel method are orthorhombic with irregularities in size and shape. The slight shoulder appearing on the peak of orthorhombic sample may be due to the asymmetric vibration in distorted lattice, and no infrared absorption occurs in the 3–5 and 8–14 μm wavebands. The εN of both samples decreases with increasing doping level, and due to stronger metallic character suggested by magnetization results, rhombohedral samples exhibit lower εN values than orthorhombic ones. The εN values in the 8–14 μm waveband are higher than those in the 3–5 μm waveband, and the εN of rhombohedral sample changes significantly in the temperature range 293–328 K. For orthorhombic sample, the εN increases slightly in the whole temperature range due to the weakening of the double-exchange interaction between Mn3+ and Mn4+.