| Abstract Scope |
Our earlier studies discovered a series of high-entropy ceramics (HECs), including single-phase equimolar five-component MB2, MB, M3B4, MB4, and MB6 borides, perovskite and YSZ-like fluorite oxides, and MSi2 and M5Si3 silicides, single-phase high-entropy intermetallic compounds that bridge high-entropy alloys (HEAs) and HECs, and dual-phase HECs. In 2020, we further proposed to extend HECs to "compositionally complex ceramics (CCCs)" to include non-equimolar compositions and long- and short-range ordering, which reduce configurational entropies, but offer additional dimensions to tailor and improve properties. See a review and perspective article [Wright & Luo, Journal of Materials Science 55: 9812-27 (2020)] and references therein. Our recent studies investigate 10- to 21-component ultrahigh-entropy fluorite-based compositionally complex oxides (CCFBOs), where long-range order-disorder transitions (e.g., fluorite-pyrochlore and pyrochlore-weberite transitions) occur but short-range orders control reduced thermal conductivity, and compositionally complex perovskite oxides (CCPOs) as new classes of materials for solar thermochemical hydrogen generation and as solid lithium-ion conductors. |