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Maximizing Misfit Cation Solubility in Rock‐Salt High‐Entropy Oxides.

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Title: Maximizing Misfit Cation Solubility in Rock‐Salt High‐Entropy Oxides.
Authors: Furst, Matthew1 (AUTHOR), Petruska, Joseph1 (AUTHOR), Srikanth, Dhiya1 (AUTHOR), Sivak, Jacob T.2 (AUTHOR), Sinnott, Susan B.1,2,3 (AUTHOR), Rost, Christina M.4 (AUTHOR), Maria, Jon‐Paul1 (AUTHOR), Almishal, Saeed S. I.1 (AUTHOR) saeedsialmishal@gmail.com
Source: Journal of the American Ceramic Society. May2026, Vol. 109 Issue 5, p1-8. 8p.
Subjects: Solubility, Calcium ions, Chemical bond lengths, Metastable states, Crystal structure, Pulsed laser deposition, Lattice constants, Oxide ceramics
Abstract: To explore and quantitatively map the cation‐size mismatch solubility limits in high‐entropy oxides (HEOs), we report on Ca2+ substitution in prototypical MgCoNiCuZnO, because while isovalent, Ca2+ is 38% larger than its partners' average ionic radii. Using the thermodynamics‐grounded bond‐length distribution descriptor, we identify Ca2+–Cu2+ interactions as the primary prospective lattice destabilizer. Bulk synthesis powder diffraction confirms at most 4% Ca2+ solubility with Cu at 950°C, modestly rising to at most 5% after Cu removal at 1150°C. We then employ far‐from‐equilibrium pulsed‐laser deposition to investigate metastable solubility; epitaxial films incorporate 10% Ca2+ with Cu and a full 20% Ca2+ without, doubling and quadrupling the respective bulk limits. Ca2+ incorporation enables deterministic control of the lattice parameter through composition, producing a 4.2% out‐of‐plane lattice expansion over a 10% Ca2+ window in MgCoNiCuZnO and a 2.6% expansion over a 20% Ca2+ window in the Cu2+‐free system. Overall, our results demonstrate both the extended solubility that is possible in HEO systems, particularly when accessing metastable states through quenching from high‐energy plasma, and that the specific constellation of solid solvent cations can be rationally engineered to leverage or minimize bond‐length distributions when largely misfit cations are added, thus expanding the accessible compositional space. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:To explore and quantitatively map the cation‐size mismatch solubility limits in high‐entropy oxides (HEOs), we report on Ca2+ substitution in prototypical MgCoNiCuZnO, because while isovalent, Ca2+ is 38% larger than its partners' average ionic radii. Using the thermodynamics‐grounded bond‐length distribution descriptor, we identify Ca2+–Cu2+ interactions as the primary prospective lattice destabilizer. Bulk synthesis powder diffraction confirms at most 4% Ca2+ solubility with Cu at 950°C, modestly rising to at most 5% after Cu removal at 1150°C. We then employ far‐from‐equilibrium pulsed‐laser deposition to investigate metastable solubility; epitaxial films incorporate 10% Ca2+ with Cu and a full 20% Ca2+ without, doubling and quadrupling the respective bulk limits. Ca2+ incorporation enables deterministic control of the lattice parameter through composition, producing a 4.2% out‐of‐plane lattice expansion over a 10% Ca2+ window in MgCoNiCuZnO and a 2.6% expansion over a 20% Ca2+ window in the Cu2+‐free system. Overall, our results demonstrate both the extended solubility that is possible in HEO systems, particularly when accessing metastable states through quenching from high‐energy plasma, and that the specific constellation of solid solvent cations can be rationally engineered to leverage or minimize bond‐length distributions when largely misfit cations are added, thus expanding the accessible compositional space. [ABSTRACT FROM AUTHOR]
ISSN:00027820
DOI:10.1111/jace.70842