Electronic structure of pristine and Ni-substituted $\mathrm{La}\mathrm{Fe}{\mathrm{O}}_{3}$ from near edge x-ray absorption fine structure experiments and first-principles simulations

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Electronic structure of pristine and Ni-substituted $La Fe O_{3}$ from near edge x-ray absorption fine structure experiments and first-principles simulations

Iurii Timrov, Piyush Agrawal, Xinyu Zhang, Selma Erat, Riping Liu, Artur Braun, Matteo Cococcioni, Matteo Calandra, Nicola Marzari, and Daniele Passerone

Phys. Rev. Research 2, 033265 – Published 19 August 2020

Abstract

We present a joint theoretical and experimental study of the oxygen $K$ -edge spectra for $La Fe O_{3}$ and homovalent Ni-substituted $La Fe O_{3}$ ( $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ ), using first-principles simulations based on density-functional theory with extended Hubbard functionals and x-ray absorption near edge structure (XANES) measurements. Ground-state and excited-state XANES calculations employ Hubbard onsite $U$ and intersite $V$ parameters determined from first principles and the Lanczos recursive method to obtain absorption cross sections, which allows for a reliable description of XANES spectra in transition-metal compounds in a very broad energy range, with an accuracy comparable to that of hybrid functionals but at a substantially lower cost. We show that standard gradient-corrected exchange-correlation functionals fail in capturing accurately the electronic properties of both materials. In particular, for $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ they do not reproduce its semiconducting behavior and provide a poor description of the pre-edge features at the O $K$ edge. The inclusion of Hubbard interactions leads to a drastic improvement, accounting for the semiconducting ground state of $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ and for good agreement between calculated and measured XANES spectra. We show that the partial substitution of Ni for Fe affects the conduction-band bottom by generating a strongly hybridized $O (2 p) − Ni (3 d)$ minority-spin empty electronic state. The present work, based on a consistent correction of self-interaction errors, outlines the crucial role of extended Hubbard functionals to describe the electronic structure of complex transition-metal oxides such as $La Fe O_{3}$ and $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ and paves the way to future studies on similar systems.

Received 8 April 2020
Accepted 29 July 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.033265

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Density of states Electronic structure

Transition-metal rare-earth alloys

DFT+U Density functional calculations Density functional theory X-ray absorption near-edge spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Iurii Timrov ^1,*, Piyush Agrawal^2,3, Xinyu Zhang^4,5,†, Selma Erat^6,7,8,9, Riping Liu⁵, Artur Braun⁶, Matteo Cococcioni¹⁰, Matteo Calandra^11,12, Nicola Marzari¹, and Daniele Passerone²

¹Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
²nanotech@surfaces Laboratory and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), Empa–Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
³Electron Microscopy Center, Empa–Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
⁴nanotech@surfaces Laboratory, Empa–Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
⁵State Key Laboratory of Metastable Material Science and Technology, Yanshan University, CN-066004 Qinhuangdao, China
⁶High Performance Ceramics Laboratory, Empa–Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dubendorf, Switzerland
⁷Department for Materials, Nonmetallic Inorganic Materials, ETH Zurich, Swiss Federal Institute of Technology, CH-8037 Zurich, Switzerland
⁸Vocational School of Technical Sciences, Department of Medical Services and Techniques, Program of Opticianry, Mersin University, TR-33343 Yenisehir, Mersin, Turkey
⁹Advanced Technology Education Research and Application Center, Mersin University, TR-33343 Yenisehir, Mersin, Turkey
¹⁰Department of Physics, University of Pavia, Via Bassi 6, I-27100 Pavia, Italy
¹¹Dipartmento di Fisica, Università di Trento, Via Sommarive 14, 38123 Povo, Italy
¹²Sorbonne Université, CNRS, Institut des Nanosciences de Paris, UMR7588, F-75252 Paris, France

^*iurii.timrov@epfl.ch
^†xyzhang@ysu.edu.cn

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Vol. 2, Iss. 3 — August - October 2020

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Condensed Matter Physics

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Figure 1
Crystal structure of (a) $La Fe O_{3}$ and (b) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ . Both structures are of the G-type AFM ordering (vertical arrows indicate the orientation of the spin on each atom). Color code: La atoms (green), Fe atoms (blue), Ni atoms (yellow), O atoms (red); blue and yellow octahedra are centered on Fe and Ni atoms, respectively. Figures were produced using the VESTA program [87].
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Figure 2
Projected density of empty states computed using DFT, $DFT + U$ , and $DFT + U + V$ for (a) $La Fe O_{3}$ and (b) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ , using Hubbard parameters listed in Table 1. The zero of energy corresponds to the valence band maximum (or Fermi energy in the case of $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ at the DFT level of theory, which comes out to be metallic). The PDOSs for $O (2 p)$ and $Ni (3 d)$ states are multiplied by a factor of 5 for easier comparison with other PDOS components; the PDOSs for $Fe (3 d)$ and $Ni (3 d)$ states show only the minority spin components on all panels since the majority spin components correspond to occupied states (see Appendix pp1). Comparison between the experimental and theoretical oxygen $K$ -edge XANES spectra of (c) $La Fe O_{3}$ and (d) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ . The energy scales for the experimental spectra of LFO and LFNO are aligned (by a rigid shift) in order to facilitate the comparison. PDOS and XANES spectra are shifted vertically for clarity.
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Figure 3
Projected density of occupied states computed using DFT, $DFT + U$ , and $DFT + U + V$ for (a) $La Fe O_{3}$ and (b) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ using Hubbard parameters listed in Table 1. The zero of energy corresponds to the valence band maximum (or Fermi energy in the case of $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ at the DFT level of theory, which comes out to be metallic). PDOS components were shifted vertically for the sake of clarity. The PDOSs for $Fe (3 d)$ and $Ni (3 d)$ states show only the majority spin components on all panels (the minority spin components correspond to unoccupied states).
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Figure 4
Projected density of empty states computed using DFT, $DFT + U$ , and $DFT + U + V$ for (a) $La Fe O_{3}$ and (b) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ , using Hubbard parameters listed in Table 4. The zero of energy corresponds to the valence band maximum (or Fermi energy in the case of $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ at the DFT level of theory, which comes out to be metallic). The PDOSs for $O (2 p)$ and $Ni (3 d)$ states were multiplied by a factor of 5 for easier comparison with other PDOS components; the PDOSs for $Fe (3 d)$ and $Ni (3 d)$ states show only the minority spin components on all panels since the majority spin components correspond to fully occupied states. Comparison between the experimental and theoretical oxygen $K$ -edge XANES spectra of (c) $La Fe O_{3}$ and (d) $La {Fe}_{0.75} {Ni}_{0.25} O_{3}$ . The energy scales for the experimental spectra of LFO and LFNO are aligned (by a rigid shift) in order to facilitate the comparison. PDOS and XANES spectra are shifted vertically for clarity.
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Physical Review Research

Electronic structure of pristine and Ni-substituted LaFeO3 from near edge x-ray absorption fine structure experiments and first-principles simulations

Iurii Timrov, Piyush Agrawal, Xinyu Zhang, Selma Erat, Riping Liu, Artur Braun, Matteo Cococcioni, Matteo Calandra, Nicola Marzari, and Daniele Passerone

Phys. Rev. Research 2, 033265 – Published 19 August 2020

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Electronic structure of pristine and Ni-substituted $La Fe O_{3}$ from near edge x-ray absorption fine structure experiments and first-principles simulations