Research On The Radiation Performance And Energy Band Structure Of Doped Lanthanum Ferrite-based Materials In The Near Mid-infrared Band

nfrared radiation material is an emerging functional material that used in industrial furnaces,infrared heating and some other fields.Under high temperature conditions,infrared radiation materials are mainly oxides,but its emissivity in the near-mid-infrared band,which was dominant in radiation heat transfer,was not high.This hinders the application of materials in industrial kilns.LaFeO₃ has outstanding high temperature resistance and oxidation resistance,and can be used as an ideal substrate.Chemical doping is the best way to improve the emissivity of materials in specific bands.Therefore,the high temperature solid phase sintering method was used to prepare LaFeO₃ single-doped powders at A and B sites.The emissivity of samples in near-mid-infrared band was measured,and which was compared with the emissivity of single-doped powders,in order to determine the A+B lattice composite doping scheme.The absorption edge of lanthanum ferrite A-doped Mg/Ca/Ba powder moves from 500nm to1940nm,and the emission sequence in the near-mid-infrared band was:Ba>Ca>Mg>LaFeO₃.The emission rate of all doped sample in near infrared band was above 0.93,and in mid-infrared band was above 0.78,which was much higher than that of LaFeO₃,which was 0.5.Combined with XPS fitting,Fe in the doped system exists in the valence of+3 and+4,resulting in a Fe³⁺?Fe⁴⁺hopping small polaron which only need 0.1eV activation energy.At the same time,the oxygen vacancy concentration increases and the lattice vibration absorption increases.The forbidden band width of the doped powder was reduced from 3.818eV of LaFeO₃ to 0eV,which promotes the impurity level absorption of the material.After the doping of Mn/Co/Cr in B-site of lanthanum ferrite,the absorption edge was sightly red-shifted.The order of emissivity in the near-mid-infrared band was:Mn>Co>Cr>LaFeO₃,and the Fe site that doped with Cr/Co has a lower proportion of valence elements,and the free carrier absorption mechanism was weaker than that of Mn doping.The band gap width of Mn/Co/Cr doping decreases from 3.817eV to 0.793eV,1.722eV and 2.406eV,respectively,mainly due to the impurity level formed by the hybridization of Mn/Cr/Co3d with O2p.At the same time,the gap width of transition was shortened by the state density peak of Mn/Cr/Co 3d in the conduction band.The emissivity of the five prepared composite doped samples increased significantly in the1-5um band,especially in the near infrared region and the mid-infrared band,reaching above 0.9and around 0.85,respectively.The order of emissivity of A+B composite co-doped specimens was Ba-Mn>Ba-Cr>Mg-Cr>Mg-Co>Mg-Mn>LaFeO₃,and the forbidden bandwidth values of Mg-Mn,Mg-Cr,Mg-Co,Ba-Mn and Ba-Cr composite doped powders were 0.482eV,0.109eV,0.027eV,0eV,0eV,0eV,respectively.which were determined by the hybrid energy level formed by the hybridization of the 3d and O2p orbitals of B lattice elements and the 3d orbital of B lattice elements on the right side of Fermi level.The mechanism of doping to enhance the emissivity of lanthanum ferrite-based materials lies in the following aspects:The increase of hopping small polaron and electron-oxygen vacancy concentration caused by element valence change belongs to the enhancement of free carrier absorption of powders;The impurity energy levels produced by doping elements at the top and bottom of the primary valence band reduce the energy required for transition from valence band to conduction band;Doping causes lattice distortion and enhances lattice non-concurrent vibration absorption.Among these theoretical mechanisms,free carrier absorption dominates the emission performance of materials in near-mid-infrared band.The lanthanum ferrite-based radiation material studied in this paper has excellent emission performance in the 1-5um band,and achieves the unification of theoretical simulation and experimental results.It has certain basic theoretical value.I hope that it can be used as reference value in China’s high-temperature energy-saving field.