Influence of thermal and atmospheric conditions on phase formation of high-entropy oxides in Co-Cu-Zn-Mn-Ni-Li-O system

Expanding the chemical complexity of materials beyond conventional compositions represents a promising strategy to address the growing demand for novel functionalities and tailored properties. This approach has led to the development of high-entropy materials, HEMs, a class of compounds characterized by the incorporation of multiple principal elements within a single-phase crystal structure. By enabling access to an expansive and largely unexplored chemical space, HEMs offer unique opportunities for the design of materials with tunable structural and functional properties. The concept was initially introduced in 2004 with high-entropy alloys (HEAs) [1], and later extended to ceramics, with the first high-entropy oxides (HEOs) reported in 2015 [2]. Since then, a wide range of HEMs have been synthesized.

This study explores the development of high-entropy rock-salt ceramics in the Li-doped Co-Cu-Zn-Mn-Ni-O system. The investigation focuses on the phase formation and stability of selected compositions synthesized via solid-state reaction and electric-field-assisted techniques, such as reaction flash sintering. This study provides a detailed comparison between both methodologies, where the influence of temperature, synthetic atmosphere as well as electric parameters is studied. Note that electric-field-assisted methodologies are of particular interest due to its adaptability to various atmospheric conditions, which can significantly impact the oxidation states of the constituent elements. The coexistence of multiple cations with distinct site preferences and potential interactions enables fine-tuning of material properties by modifying synthesis parameters. As a result, it is possible to obtain compounds with identical cation compositions but differing in crystal structure and stoichiometry.

References

[1] B. Cantor, I.T.H. Chang, P. Knight, A.J.B. Vincen , Materials Science and Engineering: A 375-377 (2004) 213-218.

[2] C.M. Rost, E. Sachet, T. Borman, A. Moballegh, E.C. Dickey, D. Hou, J.L. Jones, S. Curtarolo, J.-P. Maria, Nature communications 6(1) (2015) 8485.