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

Handle URI:
http://hdl.handle.net/10754/255454
Title:
First-principles investigation of the electronic states at perovskite and pyrite hetero-interfaces
Authors:
Nazir, Safdar
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.
Advisors:
Schwingenschlögl, Udo ( 0000-0003-4179-7231 )
Committee Member:
Alshareef, Husam N.; Amassian, Aram ( 0000-0002-5734-1194 ) ; Eppinger, Jörg ( 0000-0001-7886-7059 ) ; Manchon, Aurelien ( 0000-0002-4768-293X )
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Program:
Materials Science and Engineering
Issue Date:
Sep-2012
Type:
Dissertation
Appears in Collections:
Dissertations; Physical Sciences and Engineering (PSE) Division; Materials Science and Engineering Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorSchwingenschlögl, Udoen
dc.contributor.authorNazir, Safdaren
dc.date.accessioned2012-12-12T06:54:07Z-
dc.date.available2012-12-12T06:54:07Z-
dc.date.issued2012-09en
dc.identifier.urihttp://hdl.handle.net/10754/255454en
dc.description.abstractOxide 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.en
dc.language.isoenen
dc.subjecttwo dimensional electron gasen
dc.subjectperovskite oxidesen
dc.subjectnanoscale devicesen
dc.subjecthalf-metallicityen
dc.titleFirst-principles investigation of the electronic states at perovskite and pyrite hetero-interfacesen
dc.typeDissertationen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberAlshareef, Husam N.en
dc.contributor.committeememberAmassian, Aramen
dc.contributor.committeememberEppinger, Jörgen
dc.contributor.committeememberManchon, Aurelienen
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.nameDoctor of Philosophyen
dc.person.id102050en
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