The First-principles Calculation Of Physical Properties And Application Of Vanadata Perovskite

The oxide with perovskite unit-cell structure （ABO₃） has a lot of interestingproperties. And has been used in a large number of many aspects, such as electronics,optics, sensing, energy storage and so on. At the same time it has good developmentspace in the field of emerging electronics and spintronics. In addition, the perovskiterare earth-transition metal oxide material belongs to the strong correlation system,which contains abundant physical connotation. In recent years, it has been the keyproblem of the study of condensed matter theory, multi-body quantum mechanicaland even the emerging computational material science, such as density functionaltheory. Due to the vanadate perovskite （RVO₃, R=La, Ca, Sr, Y, Ce） has a variety ofspecial physical properties, it can be used in many fileds. This article focuses onRVO₃and using first principles calculation method and VASP package to calculate.In order to study the influence of different R ions on the material crystal structure,the electronic structure and physical properties, analyze the LaVO₃resistance tosulfur poisoning and the effect of Sr dopeding on the stability and the improvementof the structure.During calculating RVO₃structure and electronic energy band, we found thatwhen V is+4valence （R=Ca, Sr） and+3valence （R=La, Ce, Y） materials showmetallicity and Mott insulator characteristics respectively. When V ion valence issame the size of the unit cell volume is proportional to R ionic radius of A bit. WhenV is+3valence the unit cell volume is significantly greater than that of+4valence.That means V local electronic effect is important factor. Besides, A radiusdecreasing result in the octahedron frame structure under bigger pressure. It leads toV-O-V angle and distortion increase. If R is+3valence, it has strong attraction toV3+d electronic with the local state center ion. This influences the octahedron fieldand aggravates Jahn-Teller effect. While if R is+2valence, we cannot observe thisphenomenon.When study Sr doped LaVO₃we found that Sr greatly improves the electricconductivity. There are large concentrations of charge around Sr2+ions. The ions arep-type doping. They lead to new peak emergence in the forbidden band structure. Inaddition, the irons doping has significant effects on structure. It causes contractionof V-O which is belong to O-V-O structure, V local electronic decreasing and theenhancing oxygen hybridization. In this structure the charge of V ions are similarwith the SrVO₃. This provides convenience for forming independent VO₄tetrahedron structure.Based on the work above, the role of oxygen defects in the crystal latticestructure and electronic structure is studied. And we also research the relationship between Sr doped with oxygen defects. We found the gap O makes material morestable. This is in discrepancy with giving priority to interstitial oxygen in knownperovskite. However this is a good reason to explain why the Sr₃V₂O₈appear.Clearance O aggravates VO6total vertex octahedral converse to independenttetrahedral VO₄. At the same time, the Sr doped is not inhibit the production ofinterstitial oxygen. Instead, it makes VO₄independent tetrahedron more stable to acertain extent.Finally, LaVO₃surface model is established. We measure the adsorption of theH2S on the surface of LaVO₃. Come to the conclusion that it between physical andchemical adsorption. It proves that the reason why vanadate base perovskitematerials have good resistance to sulfur is the Fermi level surface structure isconsisted by V3d electronic. The hybrid in S p3electronic of H2S is difficult. Alsoin Sr₃V₂O₈structure the Sr ions concentration is higher. So in the formation processthe Sr²⁺irons migrate to the surface. By calculating we found that in thethermodynamics the Sr has the trend of surface enrichment.