First Principles Study Of The Structure And Properties Of Doped-perovskite SrMO₃（M=Mn,Hf）

In the present paper, the structural, electronic, magnetic and optical properties of Ce, Bi and Fe doped in SrMnO3, Pb doped in SrHfO3have been investigated by using pseudo-potential plane wave method within the generalized gradient approximation GGA method by first principles, respectively.Firstly, for the case of Ce doped in cubic SrMnO3, the different Mn-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6octahedron, which associate with a structural phase transition from cubic symmetry (Pm3m) to tetragonal symmetry (I4/mcm). The Jahn-Teller ordering stabilizes a chain like (C-type) anti-ferromagnetic ground state. The electronic structures indicate that SrMnO3and Sr1-xCexMnO3(x=0.125and0.25) are semiconductor and conductor, respectively. The doping of SrMnO3with cerium induces simultaneously a decrease in the electrical resistivity, which can be attributed to the formation of Mn3+ion as a result of charge compensation. The density of states (DOS) and charge density map present that there exist in hybridization between some of O bands with those of Mn and Ce bands; the bonding between Sr and O is mainly ionic yet. Density of states and magnetic moment calculations show that the formal valence state of the Ce ion is trivalence.Secondly, for the case of Bi doped in hexagonal SrMnO3, the electronic structures show that SrMnO3and Sr1-xBixMnO3(x=0.5) are insulator and conductor, respectively. The density of states (DOS) and charge density maps present the bonding of Mn-O and Bi-O is mainly covalent, whereas bonding of Sr-O is mainly ionic. The improving of the electronic conductivity can be attributed to the formation of Mn3+ion as a result of charge compensation. Each magnetic phase has been determined; the results show that both the ground state configurations of SrMnO3and Sr1-xBixMn03(x=0.5) are anti-ferromagnetic state agreeing very well with the experimental reports. The spin magnetic moments of SrMnO3and Sr1-xBixMn03(x=0.5) are obtained to investigate the magnetic properties.Thirdly, for the case of Fe doped in cubic SrMnO3, the pressure induced structural phase transition of Fe doped in SrMnO3have been investigated. The cooperative Jahn-Teller distortion is not found at zero pressure. By performing a structural phase stability analysis, the phase transition occurs between the cubic and tetragonal phase at25.0GPa. As pressure above25.0GPa, the different Mn-O and Fe-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6and FeO6octahedron, which is associate with structural transition. The Jahn-Teller distortion stabilizes a chain like anti-ferromagnetic (C-AFM) ground state. The band structures and density of states show that the electrical resistivity decreased as a result of the phase transition. The result gives an anti-ferromagnetic ground state for SrMn0.875Fe0.125O3agreeing with the experimental report.Lastly, for the case of Pb doped in cubic SrHfO3, the calculated lattice constants by minimization of the total energy are in agreement with the available experimental data. Dopant formation energy results show that Pb preferentially enters the Sr site in SrHfO3rather than Hf site which is agreement with experimental results. Band structure shows that the bandgap of Sr0.875Pb0.125Hf03is small in comparison with SrHfO3, density of states and charge density map indicate that there is covalent bonding between Hf and O, and bonding of Pb-HfO3and Sr-HfO3is ionic. In order to understand the effects on optical properties of Pb doped SrHfO3, the optical properties of SrHfO3and Sr0.875Pb0.125Hf03are calculated for radiation up to40eV.