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The Effect of Point Defects on the Electronic Density of States of ScMN2-Type (M = V, Nb, Ta) Phases
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0001-5670-7644
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0003-1785-0864
2019 (engelsk)Inngår i: Condensed Matter, ISSN 2410-3896, Vol. 4, nr 3, artikkel-id 70Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb. They are narrow-bandgap semiconductors with potentially interesting thermoelectric properties. Point defects such as dopants and vacancies largely affect these properties, motivating the need to investigate these effects. In particular, asymmetric peak features in the density of states (DOS) close to the highest occupied state is expected to increase the Seebeck coefficient. Here, we used first principles calculations to study the effects of one vacancy or one C, O, or F dopant on the DOS of the ScMN2 phases. We used density functional theory to calculate formation energy and the density of states when a point defect is introduced in the structures. In the DOS, asymmetric peak features close to the highest occupied state were found as a result of having a vacancy in all three phases. Furthermore, one C dopant in ScTaN2, ScNbN2, and ScVN2 implies a shift of the highest occupied state into the valence band, while one O or F dopant causes a shift of the highest occupied state into the conduction band.

sted, utgiver, år, opplag, sider
MDPI, 2019. Vol. 4, nr 3, artikkel-id 70
Emneord [en]
ScTaN2; YNbN2; inverse MAX phase; point defect; density of states
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-160948DOI: 10.3390/condmat4030070ISI: 000487966200001OAI: oai:DiVA.org:liu-160948DiVA, id: diva2:1361446
Merknad

Funding agencies: Swedish Research Council (VR)Swedish Research Council [2016-03365]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping U

Tilgjengelig fra: 2019-10-16 Laget: 2019-10-16 Sist oppdatert: 2019-11-04bibliografisk kontrollert
Inngår i avhandling
1. Theoretical and experimental studies of ternary and quaternary nitrides for machining and thermoelectric materials
Åpne denne publikasjonen i ny fane eller vindu >>Theoretical and experimental studies of ternary and quaternary nitrides for machining and thermoelectric materials
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Alternativ tittel[sv]
Teoretiska och experimentella studier av ternära och kvarternära nitrider för metallbearbetning och termoelektriska material
Abstract [en]

Nitrides are used as coatings and thin films for a wide range of applications. The study and use of nitrides in the recent decades have shifted towards ternary, quaternary or even higher order (complex) nitrides. There is an interest to use ternary and quaternary nitrides for machining and thermoelectric materials, because it gives the possibility to choose composition and thereby design the materials properties. This thesis presents research results on TiAlN and and TiAlN-based coatings that are used as hard coatings for machining and on ternary scandium nitrides that are of interest for thin films for thermoelectric applications. The high-pressure high-temperature behavior of cubic TiAlN deposited on cubic boron nitride has been experimentally studied. It has been shown that the spinodal decomposition, which means decomposition into cubic domains enriched in TiN and AlN, is delayed as a result of high pressure compared to ambient pressure. No chemical interaction between coating and substrate occurs. TiZrAlN has been theoretically and experimentally studied at high temperature. The results show that the when Zr-content is decreased and the Al-content is increased the decomposition route changes from nucleation and growth to spinodal decomposition. The microstructure evolution with temperature depends on the initial composition. In the case where the decompositon starts with only spinodal decomposition the microstructure at 1100 °C consists of domains that are larger than in the case where the decomposition occurs by nucleation and growth. ScMN2 (M=V, Nb, Ta) phases have been experimentally demonstrated for M=Nb and Ta in a few studies, but have not been much investigated. In this theseis, their crystal structure, stability, elastic properties, electronic structure and thermoelectric properties have been studied. At 0 K and 0 GPa it has been shown that these three phases are thermodynamically and elastically stable. Additionally, these are narrow-bandgap semiconductors and their thermoelectric properties can be tuned by doping. Pressure has a stabilizing effect on these structures. When pressure increases from 0-150 GPa the elastic constants and moduli increases in the range 53-317 %.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2019. s. 50
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1983
Emneord
materials science; thin film physics; nitrides, machining; thermoelectrics, materialvetenskap; tunnfilmsfysik; nitrider; metallbearbetning; termoelektricitet
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-155101 (URN)10.3384/diss.diva-155101 (DOI)9789176851142 (ISBN)
Disputas
2019-06-05, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2019-04-02 Laget: 2019-04-02 Sist oppdatert: 2019-10-16bibliografisk kontrollert

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The Effect of Point Defects on the Electronic Density of States of ScMN2-Type (M = V, Nb, Ta) Phases(869 kB)52 nedlastinger
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