First Principle Investigation Of La₂O₃and La₂O₃-doped Preformance

With the continuous development of quantum chemistry calculation method and the computer hardware and software, has been able as a fundamental basis to basic principles of quantum mechanics, the nature of the research system to get a variety of powerful computing capability via computer. First-principles based upon density functional theory calculation method is becoming a research method, which is independent of the experimental study and the theoretical research.La2O3as a kind of typical rare earth oxides, it has the advantages of high dielectric constant and wide band gap, and it has good thermal stability, so, it is widely used in the fields of optical glass, catalysts, ceramics and thermoelectric materials. In recent, studies have found that La2O3has a good adsorption capacity for CO2gas and it has practical significance for solving coke produce problems in the process of CH4/CO2reforming reaction.In this paper, It shows that using potential plane wave method based on first principles study of the physical properties of the rare earth oxide La2O3doped systems is feasible, the main research results are as follows:(1)Construction of La2O3model and obtain lattice constants, electronic structure, and optical properties after optimized, The results show that:the lattice constants of the optimized and experimental values are very close, but also it can be seen as indirect band-gap oxides from the energy band diagram, proof established Model and calculation methods is reasonable. Analysis of the dielectric function, absorption, reflectance spectra, absorption spectra and energy loss spectra of pure La2O3, results indicated that:in the low-energy region is dominated by the optical transitions O2p states and between states of La5d, in the high energy region is dominated by O the2p states and La5s,5p optical transitions between the states these transitions are formed by the plasma excitation(2)By using the first principle pseudo-potential plane-wave method based on the density function theory, the lattice structure, energy band structure, electron density of states and optical propertise of pure La2O3, Eu,Yb doped La2O3and Eu-Yb codoped La2O3were calculated under local density approximation. The results reveal that imaginary part of the dielectric function of pure La2O3and Eu-La2O3, Yb-La2O3,(Eu,Yb)-La2O3constant of the low-energy direction shift. As to the optical properties, the reflectance of Eu-La2O3and Yb-La2O3enhances much than pure La2O3,Absorption coefficient is significantly lower,and the absorption edge redshift trend in the visible light region. Especially, compared with Eu,Yb doped La2O3,(Eu,Yb)-La2O3has slight change in optical properties, These changes are due to Eu and Yb co-doped interaction between impurity atoms.(3) To established structure model of doped and undoped of La2O3for CO2adsorption, simulation the built models. The results reveal that:either doped or undoped adsorption structures, adsorption energy of M3is the largest, indicating M3is the most stable adsorption structure. All adsorption structure, M1is physical adsorption, M2, M3and M4are chemical adsorption, such that the surface of the CO2adsorption capacity is significantly enhanced after Al-doped, improve the adsorption capacity is not obvious after Fe-doped, but the conductivity of the surface is greatly increase.