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Charge transfer effects in (HfNbTiVZr)C – shown by ab-initio calculations and X-ray photoelectron spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0001-5445-1374
(b.Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-583 Linköping, Sweden)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.ORCID iD: 0000-0001-6162-1167
(b.Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-583 Linköping, Sweden)
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(English)In: Article in journal (Other academic) Submitted
Abstract [en]

Considering charge transfer effects and the variability of the bonding between elements with different electronegativity opens up a deeper understanding of the electronic structure and as a result many of the properties in high entropy related materials. This study investigates the importance of the diverse bonding and chemical environments when discussing multicomponent carbide materials. A combination of ab initio calculations and X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of multicomponent thin films based on the (HfNbTiVZr)C system. The charge transfer was quantified theoretically using relaxed and non-relaxed multicomponent as well as binary carbide reference structures, employing a fixed sphere model. High-resolution XPS spectra from (HfNbTiVZr)C magnetron sputtered thin films displayed core level binding energy shifts and broadening effects as a result of the complex chemical environment. Charge transfer effects and a changed electronic structure in the multicomponent material, compared with the reference binary carbides, are observed both experimentally and in the DFT simulations. The observed effects loosely follow electronegativity considerations, leading to a deviation from an ideal solid solution structure assuming non-distinguishable chemically equivalent environments. 

Keywords [en]
DFT, Magnetron sputtering, Multicomponent carbide, X-ray Photoelectron spectroscopy, Charge transfer
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-517270OAI: oai:DiVA.org:uu-517270DiVA, id: diva2:1825397
Available from: 2024-01-09 Created: 2024-01-09 Last updated: 2024-01-19
In thesis
1. Investigation of compositionally complex refractory metal based thin films
Open this publication in new window or tab >>Investigation of compositionally complex refractory metal based thin films
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The search for new and improved materials has led to the discovery and establishment of compositionally complex or high-entropy materials. The work in this thesis is focused on the investigation of new compositionally complex materials based on the refractory metals of groups 4-6. The materials in this work were synthesised using non-reactive dc magnetron sputtering and three material systems have been studied: HfNbTiVZr-C, CrTiTaWNb-C and Nb-Mo-C. In the context of compositionally complex materials, this thesis aims to contribute specifically to questions regarding (i) the prediction of phase formation and stability (ii) the chemical interaction between atoms (iii) the correlation between the material properties and compositional complexity. 

The prediction of phase formation and stability using calculated phase diagram (CALPHAD) methods was studied in the HfNbTiVZr-C system. The findings suggest that CALPHAD methods are promising predictive tools, although kinetic effects during synthesis need to be taken into consideration. Furthermore, theoretical, and experimental evidence of charge transfer effects was demonstrated within the HfNbTiVZr-C system. The results of ab initio materials simulations and X-ray Photoelectron Spectroscopy (XPS) measurements highlight the importance of understanding and considering the local chemical environment and chemical interactions in compositionally complex materials.

The approach of metal alloying according to the valence electron concentration (VEC) to tune the mechanical properties was studied in the Nb-Mo-C system. The findings show the importance of microstructural effects on the mechanical properties in the studied thin film materials, which can overshadow the compositional or VEC variations. 

The response to Xe heavy-ion irradiation was studied in the CrTiTaWNb-C system using in situ irradiation experiments. This work presents a comparison between three different compositions: a TaW-rich alloy and carbide thin film as well as a near-equimolar carbide film. The findings indicate that both microstructure and chemical homogeneity play important roles when it comes to radiation damage tolerance in compositional complex materials.

This thesis demonstrates the elaborate and multifaceted nature of compositionally complex materials. Whether it comes to the fundamental understanding or the effective implementation of a materials design tool, many factors need to be taken into consideration, including chemical interactions between the constituent elements and microstructural effects.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2355
Keywords
Magnetron sputtering, Thin films, High entropy materials, Refractory metals, Transition metal carbides
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-517268 (URN)978-91-513-2007-6 (ISBN)
Public defence
2024-03-01, Häggsalen - Ångströmlaboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2018-04834
Available from: 2024-02-07 Created: 2024-01-11 Last updated: 2024-02-07

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Osinger, BarbaraLindblad, RebeckaLewin, Erik

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