| Title: |
Role of intermediate 4f states in tuning the band structure of high entropy oxides |
| Authors: |
Abhishek Sarkar, Benedikt Eggert, Leonardo Velasco, Xiaoke Mu, Johanna Lill, Katharina Ollefs, Subramshu S. Bhattacharya, Heiko Wende, Robert Kruk, Richard A. Brand, Horst Hahn |
| Source: |
APL Materials, Vol 8, Iss 5, Pp 051111-051111-10 (2020) |
| Publisher Information: |
AIP Publishing LLC, 2020. |
| Publication Year: |
2020 |
| Collection: |
LCC:Biotechnology
LCC:Physics |
| Subject Terms: |
Biotechnology, TP248.13-248.65, Physics, QC1-999 |
| More Details: |
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-(Ce0.2La0.2Pr0.2Sm0.2Y0.2)O2−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). The O K and RE M4,5/L3 XANES indicate that the presence of Ce and Pr (in 3+/4+ states) leads to the formation of intermediate 4f energy levels between the O 2p and the RE 5d gap in HEO. It is concluded that heat treatment under reducing/oxidizing atmospheres affects these intermediate levels, thus offering the possibility to tune the bandgap energy in HEOs. |
| Document Type: |
article |
| File Description: |
electronic resource |
| Language: |
English |
| ISSN: |
2166-532X |
| Relation: |
https://doaj.org/toc/2166-532X |
| DOI: |
10.1063/5.0007944 |
| Access URL: |
https://doaj.org/article/9a9d954fdb2840bf82d0aa6217bf74c4 |
| Accession Number: |
edsdoj.9a9d954fdb2840bf82d0aa6217bf74c4 |
| Database: |
Directory of Open Access Journals |
