High-entropy fluorite oxides

• Published in: Journal of the European Ceramic Society Vol. 38; no. 10; pp. 3578 - 3584
• Main Authors: Gild, Joshua, Samiee, Mojtaba, Braun, Jeffrey L., Harrington, Tyler, Vega, Heidy, Hopkins, Patrick E., Vecchio, Kenneth, Luo, Jian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-2018
• Subjects: Fluorite oxide; Hardness; High-entropy ceramic; Sintering; Thermal conductivity; Fluorite oxide; Thermal conductivity; High-entropy ceramic; Hardness; Sintering
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2018.04.010

Eleven fluorite oxides with five principal cations (in addition to a four-principal-cation (Hf0.25Zr0.25Ce0.25Y0.25)O2-δ as a start point and baseline) were fabricated via high-energy ball milling, spark plasma sintering, and annealing in air. Eight of the compositions, namely (Hf0.25Zr0.25Ce0.25Y0.25)O2-δ, (Hf0.25Zr0.25Ce0.25)(Y0.125Yb0.125)O2-δ, (Hf0.2Zr0.2Ce0.2)(Y0.2Yb0.2)O2-δ, (Hf0.25Zr0.25Ce0.25)(Y0.125Ca0.125)O2-δ, (Hf0.25Zr0.25Ce0.25)(Y0.125Gd0.125)O2-δ, (Hf0.2Zr0.2Ce0.2)(Y0.2Gd0.2)O2-δ, (Hf0.25Zr0.25Ce0.25)(Yb0.125Gd0.125)O2-δ, and (Hf0.2Zr0.2Ce0.2)(Yb0.2Gd0.2)O2-δ, possess single-phase solid solutions of the fluorite crystal structure with high configurational entropies (on the cation sublattices), akin to those high-entropy alloys and ceramics reported in prior studies. Most high-entropy fluorite oxides (HEFOs), except for the two containing both Yb and Gd, can be sintered to high relative densities. These single-phase HEFOs exhibit lower electrical conductivities and comparable hardness (even with higher contents of softer components such as Y2O3 and Yb2O3), in comparison with 8 mol. % Y2O3-stabilized ZrO2 (8YSZ). Notably, these single-phase HEFOs possess lower thermal conductivities than that of 8YSZ, presumably due to high phonon scattering by multiple cations and strained lattices.