First Principle Study Of Doping Atoms Effects On Structural Stability And Electronic Properties Of ?-Cr₂O₃ Oxide

In the study of the anti-oxidation of heat-resistant steel, the fact that chromium is generally added to stainless steels to obtain a oxidation film rich in chromium oxide. The role of such oxide layers is to limit the inward diffusion of oxygen and/or the outward diffusion of cations. Some scholars had researched the component, structure, properties and synthetic methods through the experiment measures. Chromia, Cr₂O₃ as the major component of the passive film, forms protective layers against the matrix further be oxidized. And the Cr₂O₃ also has many other applications. Base on the these characteristics, some authors study the structure and defect of ?-Cr₂O₃, however the studies for complex mainly concern on single atom dissolved in ?-Cr₂O₃, and study the magnetism, Neel temperature and band theory and so on. However the theoretical researches about complex system of oxidation film are very few. Because that there are a great variety of heat-resistant steel, many alloy elements consist in the matrix of heat-resistant steel, such as Fe?Mo?Nb?Ni?Mn?Al?Si. However the function and influence mechanism of these alloy elements on atomic level are not very clear. To our knowledge no theoretical investigations have been carried out to determine alloying atoms effect on structural stability and electrochemical properties in the ?-Cr₂O₃ mixed oxides. In the present work, we focus on the alloy behavior of transition metals M? M=Fe, Mo, Nb, Ni, Mn, Al, Si? in the ternary ?-Cr1.5M0.5O3. The evolutions of the structural stability, electronic properties of ?-Cr_1.5M_0.5O₃?M=Fe, Mo, Nb, Ni, Mn, Al, Si?.The structural stability and electronic property of ?-Cr_1.5M_0.5O₃ with doping atoms and elemental contents are studied by first-principle calculations. The cohesive energy of ?-Cr₂O₃ with Fe, Mo, Nb, Ni, Mn, Al and Si elements, which indicates that Nb,Al,Mo and Mn atoms are effective for improving the binding ability of ?-Cr₂O₃, especially Nb in ?-Cr₂O₃ oxide. Gibbs free energy proves that these doping atoms solid solution in ?-Cr₂O₃ make the structure more stable at the temperature range of 200-1000 K, especially Ni and Si in ?-Cr₂O₃ oxide. Compared with the band gap width of ?-Cr_1.5M_0.5O₃?M= Cr, Fe, Mo, Nb, Ni, Mn, Al, Si?, Mo and Al are elements which are effective for increasing band gap width of ?-Cr_1.5M_0.5O₃, namely Mo and Al can make the structure more electrochemical stable. Furthermore, decreasing or increasing the concentration of Mo or Al in the ?-Cr₂O₃ respectively, it concludes that when the alloy concentration equals to 0.5, the ?-Cr_1.5Al_0.5O₃ and ?-Cr_1.5Mo_0.5O₃ are easier to form and the structure stability are more stable. Range from 200 K to 1000 K, with the increase of temperature to 1000 K, the structure stability of ?-Cr_1.75Al_0.25O₃ and ?-Cr_1.75Mo_0.25O₃ are more stable than the ?-Cr_1.5Al_0.5O₃ and ?-Cr_1.5Mo_0.5O₃ on the 0K.