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Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0002-8279-5163
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2044Article in journal (Refereed) Published
Abstract [en]

Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO(3), which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

Place, publisher, year, edition, pages
2017. Vol. 7, article id 2044
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-318191DOI: 10.1038/s41598-017-01151-2ISI: 000401511100051PubMedID: 28515466OAI: oai:DiVA.org:uu-318191DiVA, id: diva2:1084225
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationAvailable from: 2017-03-23 Created: 2017-03-23 Last updated: 2017-06-27Bibliographically approved
In thesis
1. Atomic short-range order, optical and electronic properties of amorphous transition metal oxides: An experimental and theoretical study of amorphous titanium aTiO2 and tungsten aWO3 solid thin-film oxides
Open this publication in new window or tab >>Atomic short-range order, optical and electronic properties of amorphous transition metal oxides: An experimental and theoretical study of amorphous titanium aTiO2 and tungsten aWO3 solid thin-film oxides
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amorphous transition metal oxides [aTMOs], have emerged as innovative functional materials for wide-ranging electronic, optical and energy-related applications. However, no systematic and broadly applicable method exists to assess their atomic-scale correlations, and since the optical and electronic processes are local structure-dependent, still there are not well-stablished mechanisms that suitably explain the physical properties of aTMOs.

This thesis presents experimental and theoretical studies of the atomic short-range order, optical and electronic properties, and state-defects induced by Li+-ion-intercalation and oxygen-vacancies in amorphous titanium aTiO2 and tungsten aWO3 thin-film oxides. Those properties play a key role for application in high energy-density Li+-ion batteries and in switchable dynamical modulation of solar-irradiation transmittance for energy efficient "smart windows", where the disorder-dependent Li+-ion-intercalation and oxygen-vacancy-induced defect-states influence charge-carrier transfer mechanisms. After introducing the scope of this thesis, the fundamental theoretical concepts describing the experimental findings on amorphous solids are reviewed. Thereafter, a comprehensive analysis on the optical absorption phenomena experimentally observed in oxygen-deficient and Li+-ion-intercalated aLixTiO2−y and aLixWO3−y thin-films and a discussion on the electrochromic properties are presented. The optical absorption is described in the framework of the small polaron absorption model.

Finally, a state-of-the-art systematic procedure involving theory and experiment in a self-consistent computational framework is implemented to unveil the atomic-scale structure of aTiO2 and aWO3, and its role for the electronic properties. The procedure is based in Reverse Monte Carlo [RMC] and Finite Difference Method [FDM] simulations of X-ray-Absorption spectra to construct a disordered theoretical model having the same bonding and coordination distribution as the experimental system. Ab-initio molecular dynamics simulations and density functional theory are then used to assess defect-states induced by Li+-ion-intercalation and oxygen-vacancies in aTiO2 and aWO3 oxides.

The schemes introduced in this study offer a consistent route to experimentally and theoretically assess the role of the atomic-scale structure on the optical and electronic properties of aTiO2 and aWO3 and could be extended to the study of other aTMOs. The final results provide crucial insight towards the understanding of optical and electronic mechanisms where disorder-dependent ion-intercalation and oxygen-vacancy-induced localized defect-states influence charge transfer mechanisms of crucial importance for wide ranging optical and energy-related application of aTiO2 and aWO3 oxides.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 150
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1493
Keywords
X-ray-Absorption, Reverse Monte Carlo, Molecular dynamics, Electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-318193 (URN)978-91-554-9866-5 (ISBN)
Public defence
2017-05-15, Room Å80101, Lägerhyddsv. 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2017-04-24 Created: 2017-03-23 Last updated: 2017-05-05

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