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    First-principles investigation of the electronic states at perovskite and pyrite hetero-interfaces

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    S_Nazir_Diss_12.10.12.pdf
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    Description:
    Dissertation
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    Type
    Dissertation
    Authors
    Nazir, Safdar
    Advisors
    Schwingenschlögl, Udo cc
    Committee members
    Alshareef, Husam N. cc
    Amassian, Aram cc
    Eppinger, Jörg cc
    Manchon, Aurelien cc
    Program
    Materials Science and Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2012-09
    Permanent link to this record
    http://hdl.handle.net/10754/255454
    
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    Abstract
    Oxide heterostructures are attracting huge interest in recent years due to the special functionalities of quasi two-dimensional quantum gases. In this thesis, the electronic states at the interface between perovskite oxides and pyrite compounds have been studied by first-principles calculations based on density functional theory. Optimization of the atomic positions are taken into account, which is considered very important at interfaces, as observed in the case of LaAlO3/SrTiO3. The creation of metallic states at the interfaces thus is explained in terms of charge transfer between the transition metal and oxygen atoms near the interface. It is observed that with typical thicknesses of at least 10-12 °A the gases still extend considerably in the third dimension, which essentially determines the magnitude of quantum mechanical effects. To overcome this problem, we propose incorporation of highly electronegative cations (such as Ag) in the oxides. A fundamental interest is also the thermodynamic stability of the interfaces due to the possibility of atomic intermixing in the interface region. Therefore, different cation intermixed configurations are taken into account for the interfaces aiming at the energetically stable state. The effect of O vacancies is also discussed for both polar and non-polar heterostructures. The interface metallicity is enhanced for the polar system with the creation of O vacancies, while the clean interface at the non-polar heterostructure exhibits an insulating state and becomes metallic in presence of O vacancy. The O vacancy formation energies are calculated and explained in terms of the increasing electronegativity and effective volume of A the side cation. Along with these, the electronic and magnetic properties of an interface between the ferromagnetic metal CoS2 and the non-magnetic semiconductor FeS2 is investigated. We find that this contact shows a metallic character. The CoS2 stays quasi half metallic at the interface, while the FeS2 becomes metallic. At the interface, ferromagnetic ordering is found to be energetically favorable as compared to antiferromagnetic ordering. Furthermore, tensile strain is shown to strongly enhance the spin polarization so that a virtually half-metallic interface can be achieved, for comparably moderate strain. Our detailed study is aimed at complementing experiments on various oxide interfaces and obtaining a general picture how factors like cations, anions, their atomic weights and elecronegativities, O vacancies, lattice mismatch, lattice relaxation, magnetism etc play a combined role in device design.
    Citation
    Nazir, S. (2012). First-principles investigation of the electronic states at perovskite and pyrite hetero-interfaces. KAUST Research Repository. https://doi.org/10.25781/KAUST-67458
    DOI
    10.25781/KAUST-67458
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-67458
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program

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