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

Robert Pilemalm,Per Eklund,Sergei Simak

doi:10.3390/condmat4030070

Robert Pilemalm, Per Eklund + Show 1 more

Open Access

https://doi.org/10.3390/condmat4030070

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Journal: Condensed Matter	Publication Date: Jul 15, 2019
Citations: 6	License type: CC BY 4.0

Affiliation: Thinfilm (Sweden), Linköping University

Abstract

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.

Highlights

Vacancies, dopants, and other point defects are important for controlling or tuning the properties of materials [1,2,3]
In the case of one F dopant to be introduced, it can be noted that the formation energies were positive in the cases of ScTaN2 and ScNbN2
This should initially decrease the absolute values of the Sxx and Szz components of ScNbN2 and ScVN2 followed by a sign reversal, while the change of these components is expected to be less pronounced for ScTaN2

Summary

Introduction

Dopants, and other point defects are important for controlling or tuning the properties of materials [1,2,3]. The electronic structure close to the Fermi level in the DOS of a thermoelectric material can be affected by the introduction of defects or impurities, which in turn alter the conductivity (σ), and may improve the thermoelectric power factor (S2σ) and maximize the figure of merit (ZT). We proposed, based on ab initio calculations, that ScTaN2, ScNbN2, and ScVN2 could be of interest in this context We found that these materials have anisotropic thermoelectric properties that can be tuned by doping [22]. We investigate the effect of one vacancy or one dopant on the electronic DOS close to the highest occupied state of ScTaN2, ScNbN2, and ScVN2

Computational Details

Results and Discussion

Conclusions