Metal-insulator transition in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ with intrinsic defects

Metal-insulator transition in $V_{2} O_{3}$ with intrinsic defects

Richard Tran, Xiang-Guo Li, Shyue Ping Ong, Yoav Kalcheim, and Ivan K. Schuller

Phys. Rev. B 103, 075134 – Published 19 February 2021

Abstract

Vanadium sesquioxide ( $V_{2} O_{3}$ ) is a Mott insulator exhibiting a temperature-dependent metal-insulator transition (MIT) at 165 K accompanied by both a magnetic and structural transition. Although it is expected to be a metal under conventional band theory, electron interactions at low temperature cause it to behave like an insulator, making it difficult to accurately model its electronic properties with standard ab initio methods. As such, accurate theoretical assessments of the MIT with point defects requires special attention to the type of functionals used. In this study, we conclude that the $PBE + U$ functional provides the best compromise between accuracy and efficiency in calculating the properties related to the MIT between low-temperature and high-temperature $V_{2} O_{3}$ . We use this functional to explore the various influences that intrinsic point defects will have on the MIT in $V_{2} O_{3}$ .

Received 13 October 2020
Revised 27 January 2021
Accepted 1 February 2021

DOI:https://doi.org/10.1103/PhysRevB.103.075134

Physics Subject Headings (PhySH)

Antiferromagnetism Density of states Ferromagnetism Metal-insulator transition Peierls transition Point defects Thermodynamics

Density functional theory

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Richard Tran, Xiang-Guo Li, and Shyue Ping Ong ^*

Department of NanoEngineering, University of California San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA

Yoav Kalcheim

Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel

Ivan K. Schuller

Department of Physics and Center for Advanced Nanoscience, University of California San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA

^*ongsp@eng.ucsd.edu

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Vol. 103, Iss. 7 — 15 February 2021

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Figure 1
Conventional unit cells of (a) the LT monoclinic ( $I_{2} / a$ ) and (b) the HT corundum ( $R \bar{3} c$ ) phases of $V_{2} O_{3}$ . The Wyckoff symbols and spin directions (large red/blue spheres correspond to opposite spins) of each symmetrically distinct site are given on the right of each structure.
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Figure 2
Plots of the band gap of (a) the LT AFI phase of $V_{2} O_{3}$ and (b) the energy difference per formula unit relative to the HT FM phase for the PBE, $PBE + U$ , SCAN, $SCAN + U$ , and HSE functionals. The $U$ parameters of 2.68 and 1.35 eV for $PBE + U$ and $SCAN + U$ , respectively, were calibrated to reproduce the experimental band gap of LT $V_{2} O_{3}$ . The dashed black line indicates the experimental band gap, and the blue shaded region indicates the expected energy difference for $V_{2} O_{3}$ .
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Figure 3
Stability map for charged and neutral defects in LT $V_{2} O_{3}$ as a function of $ɛ_{F}$ and $Δ μ_{O}$ . The legend at the top indicates the colors representing defect types. The lighter red region indicates where the formation of vanadium-deficient $V_{2} O_{3}$ is favorable relative to stoichiometric $V_{2} O_{3}$ , i.e., $E_{form} < 0$ eV, while the solid red region indicates $E_{form} > 0$ eV. Vertical dashed lines indicates a transition between charged states in a defect. Two corresponding temperature scales derived from the JANAF thermochemical tables [39] are provided as the secondary $y$ axis on the right [see the Supplemental Material 25]. The temperature scales are based on two partial pressures of oxygen: $p_{0} = 0.1$ MPa, i.e., standard atmospheric conditions, and $p_{0} = 10^{- 13}$ MPa, i.e., ultrahigh-vacuum conditions (parentheses).
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Figure 4
Total (green), O- $2 p$ (blue), and V- $3 d$ (red) orbital DOS for a $2 \times 2 \times 2$ supercell of (a) LT stoichiometric $V_{2} O_{3}$ and nonstoichiometric $V_{2} O_{3}$ containing a (b) $v_{V}$ , (c) $v_{V}^{'}$ , (d) $v_{O}^{•}$ , or (e) $v_{O}$ defect. The VBM and CBM of the nonstoichiometric $V_{2} O_{3}$ (black dashed lines) as well as the Fermi level (black solid line) are also provided for each DOS. The stoichiometric VBM and CBM (gray dashed lines) are also provided for reference. The corresponding activation energies for carrier conductivity ( $E_{a}$ ), i.e., the energy difference between the stoichiometric CBM and transition levels (dashed lines), are also annotated in (b) (red) and (d) (blue).
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Figure 5
The $2 \times 2 \times 2$ supercell of $V_{2} O_{3}$ containing $v_{V}$ (a) and $v_{O}$ (b). All sites with Bader charges that differ from bulk-like charges are labeled, while all other sites have bulk-like charges. Bulk-like charges are labeled on the top left sites for oxygen ( $- 1.24$ ) and vanadium ( $+ 1.87$ ).
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Figure 6
The neutral defect formation energy ( $E_{form}$ ) for $O_{i}$ , $V_{i}$ , $v_{V}$ , and $v_{O}$ in LT AFI (solid) and HT FM (dashed) $V_{2} O_{3}$ as a function of the oxygen chemical potential ( $Δ μ_{O}$ , top $x$ axis). The temperature scales based on $p_{0} = 0.1$ ( $p_{0} = 10^{- 13}$ MPa in parentheses) is provided on the bottom $x$ axis.
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Physical Review B

covering condensed matter and materials physics

Metal-insulator transition in $V_{2} O_{3}$ with intrinsic defects

Richard Tran, Xiang-Guo Li, Shyue Ping Ong, Yoav Kalcheim, and Ivan K. Schuller

Phys. Rev. B 103, 075134 – Published 19 February 2021

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Physical Review B

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Metal-insulator transition in V2O3 with intrinsic defects

Richard Tran, Xiang-Guo Li, Shyue Ping Ong, Yoav Kalcheim, and Ivan K. Schuller

Phys. Rev. B 103, 075134 – Published 19 February 2021

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Metal-insulator transition in $V_{2} O_{3}$ with intrinsic defects