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First Principles Investigations of the Structure and Properties of Doped-perovskite SrMO3（M=Ru,Ti）

Author: JiaoPeng
Tutor: WangXueYe
School: Xiangtan University
Course: Physical and chemical
Keywords: Doping First principles Magnetic moment Perovskite Elastic constants
CLC: O641
Type: Master's thesis
Year: 2013
Downloads: 43
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Abstract


In this paper, the structural, electronic, magnetic and properties of the follow systems:SrRuO3/SrTiO3/SrRuO3, Na and Fe doped in SrRuO3, Ru doped in SrTiO3are investigatedby first principles, respectively.Firstly, for the SrRuO3/SrTiO3/SrRuO3, the case of oxygen vacancy sites formationenergies of five different models, are studied with the pseudo-potential plane wave methodwithin the generalized gradient approximation （GGA） and GGA+U, can be semiquantitatively described of metal-oxygen bonds broken and lattice mismatch in theinterface. The calculational results indicate that the distribution of the oxygen vacancy ismainly concentrated the interface of the crystal growth. Furthermore, the electronicproperties of the model which has lowest oxygen vacancy formation energy are evaluated.Secondly, The structural, electronic, and elastic properties of Ru dropped the cubicperovskite SrTiO3are investigated using density-functional theory within both local densityapproximation （LDA） and generalized gradient approximation （GGA）.The average value ofoptimized lattice constant for SrRu0.125Ti0.875O3is3.927, which larger than SrTiO3（average value of optimized lattice is3.895） due to the ionic size of Ti4+（0.605） andRu4+（0.620）. The electronic structure shows that Fermi level of the SrRu0.125Ti0.875O3moves into the top of valence band. Ru doping can increase the density of states at Fermilever. Then the system undergoes an insulator-to-metal transition. Furthermore, the bulkmodulus B（GPa）, isotropic shear modulus G（GPa）, elastic constants Cij（GPa）, theanisotropy factor A, and Debye temperature（TD） for SrTiO3and SrTi0.875Ru0.125O3arepredicted.Thirdly, for the case of Na doped SrRuO3, the structural, electronic and magneticproperties of Na doped SrRuO3have been investigated using the pseudo-potential planewave method within the generalized gradient approximation GGA+U method by firstprinciples. The results show that all structures of Sr1-xNaxRuO3(x=0,0.125,0.25) areferromagnetic phase. There is a more strong Jahn-Teller distortion of the RuO6octahedra inNa doped compounds. Na doping cannot induce magnetic phase transition in SrRuO3, butcan lead to a reduction of effective magnetic moment, which predominately due to Stonermechanism for ferromagnetism in SrRuO3is weakened by Na doping. Na doping can lowerthe density of states at Fermi lever and decrease the number of electrons above the Fermi energy which indicated that the pure SrRuO3is more metallic than Sr0.875Na0.125RuO3andSr0.75Na0.25RuO3. However, the metal-insulator transition has not happened when Na onlysubstituted on the Sr site in SrRuO3.Lastly, for the case of Fe doped SrRuO3, Dopant formation energy results predict thatFe preferentially enters the Ru site in SrRuO3rather than Sr site which is agreement withexperimental results. The calculated lattice constants by minimization of the total energyare in agreement with the available experimental data. Density of states and electronicstructure show that the Fe doping can increase the resistance of SrRuO3.

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