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Role of intermediate 4f states in tuning the band structure of high entropy oxides

Sarkar, Abhishek; Eggert, Benedikt; Velasco, Leonardo; Mu, Xiaoke; Lill, Johanna; Ollefs, Katharina; Bhattacharya, Subramshu S.; Wende, Heiko; Kruk, Robert; Brand, Richard A.; Hahn, Horst

High entropy oxides (HEOs) are single-phase solid solutions consisting of 5 or more cations in approximately equiatomic proportions. In this study, we show the reversible control of optical properties in a rare-earth (RE) based HEO-(Ce$_{0.2}$La$_{0.2}$Pr$_{0.2}$Sm$_{0.2}$Y0.2)O$_{2−δ}$ and subsequently utilize a combination of spectroscopic techniques to derive the features of the electronic band structure underpinning the observed optical phenomena. Heat treatment of the HEO under a vacuum atmosphere followed by reheat treatment in air results in a reversible change in the bandgap energy, from 1.9 eV to 2.5 eV. The finding is consistent with the reversible changes in the oxidation state and related f-orbital occupancy of Pr. However, no pertinent changes in the phase composition or crystal structure are observed upon the vacuum heat treatment. Furthermore, annealing of this HEO under a H2 atmosphere, followed by reheat treatment in air, results in even larger but still a reversible change in the bandgap energy from 1.9 eV to 3.2 eV. This is accompanied by a disorder–order type crystal structure transition and changes in the O 2p–RE 5d hybridization evidenced from x-ray absorption near-edge spectra (XANES). ... mehr

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Verlagsausgabe §
DOI: 10.5445/IR/1000120217
Veröffentlicht am 16.06.2020
DOI: 10.1063/5.0007944
Web of Science
Zitationen: 3
Zitationen: 7
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Nanotechnologie (INT)
Karlsruhe Nano Micro Facility (KNMF)
Publikationstyp Zeitschriftenaufsatz
Publikationsmonat/-jahr 05.2020
Sprache Englisch
Identifikator ISSN: 2166-532X
KITopen-ID: 1000120217
HGF-Programm 37.01.01 (POF III, LK 01) Fundamentals and Materials
Erschienen in APL materials
Verlag American Institute of Physics (AIP)
Band 8
Heft 5
Seiten Art.Nr. 051111
Schlagwörter 2019-023-028229, TEM, FIB
Nachgewiesen in Web of Science
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