High-Entropy Oxides in the Mullite-Type Structure

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High-entropy materials (HEMs) represent a new class of solid solutions containing at least five different elements. Their compositional diversity makes them promising as platforms for the development of functional materials. We synthesized new HEMs in a mullite-type structure and present five compounds, i.e., Bi2(Al0.25Ga0.25Fe0.25Mn0.25)4O9 and A2Mn4O10 with variations of A = Nd, Sm, Y, Er, Eu, Ce, and Bi, demonstrating the vast accessible composition space. By combining scattering, microscopy, and spectroscopy techniques, we show that our materials are mixed solid solutions. Remarkably, when following their crystallization in situ using X-ray diffraction and X-ray absorption spectroscopy, we find that the HEMs form through a metastable amorphous phase without the formation of any crystalline intermediates. We expect that our synthesis is excellently suited to synthesizing diverse HEMs and therefore will have a significant impact on their future exploration.

Original languageEnglish
JournalChemistry of Materials
Issue number20
Pages (from-to)8664−8674
Number of pages11
Publication statusPublished - 2023

Bibliographical note

Funding Information:
This work is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (grant agreement no. 804066). We are grateful to the Villum Foundation for financial support through a Villum Young Investigator grant (VKR00015416). J.K.M. acknowledges funding from VILLUM FONDEN, research grant (41388). Funding from the Danish Ministry of Higher Education and Science through the SMART Lighthouse is gratefully acknowledged. We acknowledge support from the Danish National Research Foundation Center for High-Entropy Alloy Catalysis (DNRF 149). The Danish Research Council is acknowledged for covering travel expenses in relation to the synchrotron experiment (DanScatt). A.K. gratefully acknowledges the Deutsche Forschungsgemeinschaft (DFG, German science foundation) for funding of the project Ki 2427/1-1 (# 429360100). We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III beamlines P02.1 and P21.1. We would like to thank Dr. Soham Banerjee for assistance in using beamline P21.1 and Dr. Martin Etter and Dr. Alexander Schökel for assistance in using beamline P02.1. Beamtime was allocated for proposals I-20200547 and I-20210486 EC. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We thank Dr. Jue Liu for collecting data at beamline NOMAD. Beamtime was allocated for proposal IPTS-24814. This work is partly based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities, and we would like to thank Dr. Dragos Stoian for assistance in using beamline BM31 (SNBL). We acknowledge Assoc. Prof. Heloisa Bordallo and Dr. Mathias Dowds from University of Copenhagen, Denmark, for assistance in collecting Raman and infrared spectra. The Raman microscope used in this work was financed by the Carlsberg grant CF19-0521.

Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society.

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