Journal
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
Volume 41, Issue 13, Pages 6660-6669Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jeurceramsoc.2021.06.014
Keywords
High entropy oxides (HEO); X-ray absorption spectroscopy (XAS); Phase transformation; Valence state; Coordination state
Categories
Funding
- DOE Office of Science User Facility [DE-AC02-05CH11231]
- National Science Foundation [DMR-1745450, CMMI-2029966]
- UCI Samueli School of Engineering
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Entropy-stabilized oxides exhibit reversible entropy-driven phase transformations, allowing for property optimization and novel functionalities through the adjustment of electronic structures. The transition of Cu, Co, and Zn ions from six-fold to four-fold coordination structures in the entropy-stabilized phase is influenced by the segregation of Cu-rich tenorite phase and Co-rich spinel phase.
Entropy-stabilized oxides (ESO) display a reversible entropy-driven phase transformation that can be leveraged to produce a continuum of metastable phase states, allowing for property optimization and novel functionalities. X-ray absorption spectroscopy reveals that entropic stabilization extends to the electronic structure (valence state and cation coordination) in sintered (Co,Cu,Mg,Ni,Zn)O, manifesting as a tunable lattice distortion in the entropy-stabilized phase. Co, Cu, and Zn ions reversibly transform from six-fold to four-fold coordinated structures and from low to high valence states due to the competition between electronic structures that are equilibrium and enthalpy-driven or metastable and entropy-driven. The segregation of a Cu-rich tenorite phase and a Co-rich spinel phase influences the electronic structure evolution. ESOs can adjust their electronic structures through heat treatment, providing a powerful tool for developing functional properties. These results indicate that the definition of entropy stabilization should include entropy-stabilized electronic structures, providing motivation to reassess previously studied HEO materials.
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