关键词: 钙钛矿, 掺杂, 红外发射率, 禁带宽度, 红外辐射材料

Abstract:

LaFeO₃ and LaFe_0.75X_0.25O₃ (X=Co/Cr/Mn) samples were prepared via a high temperature solid phase sintering method. The samples were characterized through XRD, FTIR, SEM and XPS at the same time. The electronic band structure and optical properties of these samples were calculated using the CASTEP module. The results showed that the lattice was distorted, and the lattice symmetry was reduced after doping Co/Cr/Mn ions. The emissivity in the range of near-mid-infrared was as following: Mn-doped＞Co-doped＞Cr-doped＞pure LaFeO₃. The emissivity of LaFe_0.75Mn_0.25O₃ was 0.8722 and 0.6755 in the 0.2～2.5μm and 2.5～5μm bands, respectively, which were much bigger than that of pure LaFeO₃ with approximately 0.5 in the near-mid-infrared band. The mechanism of improvements in emission performance was analyzed. By doping Mn ions, the small Mn³⁺?Mn⁴⁺ hopping polaron with low activation energy was generated, electron-oxygen vacancy carrier absorption was enhanced, and the lattice distortion of Mn-doped sample caused an increase in the vibration absorption. The first-principles calculation results revealed that the forbidden band width of LaFeO₃ doped with Mn/Cr/Co were 0.793eV, 2.406eV and 1.722eV, respectively, all lower than 3.818eV of pure LaFeO₃. Combining with the analysis of state density calculation results, it was mainly because Mn3d, Cr3d, Co3d and O2p orbitals were hybridized to form impurity levels. Also, the orbitals of Mn3d, Cr3d and Co3d occurred state density peaks in the conduction band, where peak positions were much closer to the Fermi energy level than that of LaFeO₃, which shorten the gap width between valence band top and conduction band bottom. The LaFe_0.75Mn_0.25O₃ had good radiation performance in the near-mid-infrared region and showed potential for application in a high-temperature furnace.

Key words: perovskite, doping, infrared emissivity, forbidden band width, infrared radiation material