Rare-earth Burning The Glauconite Geometry And Electronic Structure Of The First Principle Studies,

Pyrochlore structured oxides A2B2O7, in which A and B are metallic cations that can either be trivalent and tetravalent or divalent and pentavalent. It encompasses a remarkable range of compounds, show a variety of physical, chemical and electrical properties including high ionic conductivity, superconductivity, luminescence, and ferromagnetism.This leads to their significant technical implementations, such as solid electrolyte, oxygen gas sensor, and fuel cells in space.Specially, radiation damage experiments suggested that pyrochlore structured oxides can be used as host matrices for actinide wastes, particularly for Pu.Along with the quickly improved computation theory and method in recent years, the Density Functional Theory (DFT) has achieved a rapid progress, and it has been used to explore the pyrochlore system. So far, first-principles method has proved to be an effective tool for investigating fundamental understanding of the structural, electronic and energetic properties of materials. In this paper, systematic calculation of structural and electronic properties of pyrochlore oxide materials has been carried out by periodic DFT theory.1. First-principles method has been employed to calculate the structural and energetic properties for A2Ti2O7 (A =Lu, Er, Y, Gd, Sm, Nd, La ), including cation antisite, Frenkel-pair, coupled cation-antisite and Frenkel-pair defect formation energies, and band gaps. It was proposed that the interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the interactions are relatively much stronger than the interactions. Also, it was found that the defect formation energies are not simple functions of A-site cation radii. The cation antisite defect formation energy increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of A-site cation from Gd to La, in excellent agreement with the trend of resistance behavior of titanate pyrochlores to irradiation induced amorphization.2. First-principles method has been employed to calculate the structural and energetic properties on A2Zr2O7(A = Gd, La, Sm, Nd)compounds to investigate their stabilities and phase transition behavior. In this paper, the calculated structural properties are in good agreement with experimental results. According to the calculated formation energies results of cation antisite, Frenkel-pair and coupled cation antisite/Frenkel-pair in pyrochlore compounds, we find that for La2Zr2O7, the defect formation energy is larger than the other compounds, which means that under irradiation, La2Zr2O7 is hard to form defect-fluorite structure, and then it would easily be amorphisized. This conclusion is agree well with experimental results. Also, we noted that the coupled cation antisite/Frenkel-pair defect formation energies are very low for the calculated compounds, indicating that these pyrochlore materials are resistant to amorphization under irradiation environment. Also, it was found that the defect formation energies are not simple functions of A-site cation radii.