First Principle Study On The Influence Of The Electronic Structure In Doping Lanthanum Chromate

In this thesis,the electronic structures of undoped,A-site doped and B-site doped lanthanum chromate materials are studied by using the first-principles method based on density functional theory.The micro-mechanism of the effect of doping on the electronic structure and the law of the influence on the conductivity of the materials are revealed,which lays a foundation for the development and utilization of Lanthanum chromate materials.After analyzing the band structure,electron density of states,overlapping population,Mulliken charge population and differential charge density obtained by self-consistent calculation,the main conclusions are as follows:(1)The model of undoped lanthanum chromate was constructed and the electronic structure of the system without doping was studied.La-doped lanthanum chromate is an indirect band-gap semiconductor material.Both valence band and conduction band near Fermi level are composed of spin-alpha electronic energy levels;the valence band range-8?0 eV is mainly composed of 3d state of Cr bonded to 2p state of O;the conduction band range 0?6 eV is composed of 5d,3d and 2p state of La bonded to O.For ionic bond,the Cr-O bond is covalent bond.(2)Three models of lanthanum chromate with different Ca doping concentration are constructed.After Ca substitution doping La,the cell volume of lanthanum chromate decreases and the lattice constant distorts at the Ca doping position.The valence band and conduction band near the Fermi level are still composed of spin-alpha electronic levels.After Ca substitution doping,the Fermi level enters the valence band and the material becomes p-type.Doped semiconductors;with the increase of Ca doping concentration,the gap between the top of valence band and the bottom of conduction band decreases gradually,and the conductivity of the material increases,which is consistent with the experimental results in the literature.From the analysis of the distribution of electronic density of states,it is found that Ca doping affects the distribution of the density of states of the 3d orbital electrons of Cr atoms.The double exchange theory:the bond length of Ca-0 bond is longer than that of La-0 bond.The Ca-0 bond is an ion bond.(3)Three kinds of lanthanum chromate models with different Mn doping concentration are constructed.After Mn substitution doping with Cr,the cell volume of lanthanum chromate becomes larger and the lattice constant distorts at the Mn doping position.The valence band and conduction band near the Fermi level are composed of spin-alpha electronic levels.After Mn substitution doping,the Fermi level enters the valence band and the material becomes p-type doping.Hybrid semiconductors;With the increase of Mn doping concentration,the bandwidth near Fermi level becomes wider,the effective mass of electrons decreases,and the acceleration is easily obtained by external field action,so the conductivity of materials is enhanced.It is found that the doping of Mn has little effect on the electron transfer of La and Cr atoms,and Mn mainly affects O.The length of Mn-O bond is longer than that of Cr-O bond.The Mn-O bond is covalent.