The effect of K+, Na+ doping on infrared emissivity of lanthanum manganites

The monovalent-doped lanthanum manganites La1−xAxMnO3 (A=K and Na, 0.1 ≤ x ≤ 0.4 ) were prepared by a standard solid-state reaction method. The structure, infrared absorption, electron spin resonance (ESR) and infrared normal emissivity ( ε N ) in the 8–14 μm waveband of the samples were systematically investigated. The samples are distorted rhombohedrals, and the formation of K4MnO4andNa4MnO4 indicates that the solubility of K+ and Na+ ions in the system is low. Infrared absorption peaks around 927 cm−1 lead to high emissivity value of the samples in the 8–14 μm waveband, and the ε N of the samples decreases with increasing doping level. K+ doped samples exhibit higher infrared emissivity value, due to higher transition probabilities indicated by the ESR spectra. The ε N of the samples remains constant in the temperature range 293–373 K.