(Mg,Cr)共掺LaFeO3基复合粉体的能带结构及其热辐射性能

Energy Band Structure and Thermal Radiation Properties of （Mg,Cr） Codoped LaFeO3 Based Composite Powders

采用高温固相烧结法在1300℃反应2 h成功制备出钙钛矿型LaFe0.75Cr0.25O3和La0.75Mg0.25Fe0.75-Cr0.25O3粉体材料。通过XRD、FT-IR、SEM、XPS和Upward IntegratIRTM等对材料的物相结构和近中红外波段的发射性能进行分析表征,并应用第一性原理计算分析了其电子结构,研究影响发射率的理论机制。研究表明,粉体在1~5μm波段的发射率都出现上升,但Cr单掺试样的吸收率增幅不大,而Mg-Cr共掺粉体增幅较大,在近红外波区的吸收率在0.9以上。究其原因在于,Cr单掺后晶体发生畸变,但不增加自由载流子的浓度,Mg-Cr共掺后畸变加剧且生成较多氧空位和小极化子,强化了自由载流子的吸收。Cr3d轨道与O 2p所形成的杂化能级和在近费米能级导带区的Cr3d轨道造成了粉体禁带宽度变窄,Mg虽然未直接作用于带隙值,但间接改变了B位元素的形态,产生了更多的小极化子,因此与LaFeO3禁带宽度值(3.817 eV)相比,Mg-Cr共掺(0.109 eV)减小幅度最大,Cr单掺(2.406 eV)次之。

Perovskite type LaFe0.75Cr0.25O3 and La0.75Mg0.25Fe0.75Cr0.25O3 powders were prepared by high temperature solid state reaction at 1300℃for 2 h.In order to study the theoretical mechanism affecting the emissivity,the phases structure of the material and the emission characteristics in near-infrared band were analyzed and characterized by XRD,FT-IR,SEM,XPS and Upward IntegratIRTM etc,the electronic structure was analyzed by first-principles calculation.The results show that the emissivity of the powder in the 1-5μm band increases,but the absorption rate of the Cr single-doped sample increases little,while the Mg-Cr co-doped powder increases greatly,and the absorption rate in the near-infrared above 0.9.The reason is that the crystal is distorted after Cr single-doped,but the concentration of free carriers does not increase.After Mg-Cr co-doped,the distortion is intensified and more oxygen vacancies and small polarized molecules are formed,which enhance the free carriers absorbtion.The hybrid energy level that formed by orbitals of Cr 3 d and O 2 p causes the powder forbidden band width to be narrowed,the same as the Cr 3 d orbital in the near-Fermi level conduction zone.Although Mg does not directly affect the band gap value,it indirectly changs the morphology of B-position elemens,and more small polarized molecules are produced.Therefore,comopared with the LafeO3 band gap value(3.817 eV),the Mg-Cr co-doped(0.109 eV)has the largest decrease,and the single-adoped(2.406 eV)secondly.