  This study discovers a reversible order-disorder transition (ODT) in a
10-cation compositionally complex ceramic,
(Nd0.15Pr0.15Dy0.8Ho0.8Er0.8Ti0.2Yb0.1Hf0.1Zr0.1Nb0.8)O7-delta, induced via
annealing in oxidized vs. reduced environments at 1600C. Notably, the 10-cation
oxide remains a homogenous single-phase high-entropy solid solution before and
after the ODT in the pyrochlore vs. fluorite structure that can be quenched.
In-situ neutron diffraction reveals the oxygen vacancy formation and atomic
displacement during this ODT. The temperature dependence of thermal
conductivity is altered by the ODT. This study reveals a new pathway to induce
ODT via a redox transition to tailor the properties of compositionally complex
fluorite-based oxides.
