Single-phase duodenary high-entropy fluorite/pyrochlore oxides with an order-disorder transition

Improved thermomechanical properties have been reported for various high-entropy oxides containing typically five metal cations. This study further investigates a series of duodenary (11 metals + oxygen) by mixing different fractions five-cation fluorite-structured niobate and seven-cation pyrochlore (both Yb) with matching lattice constants. Nine compositions examined. All them exhibit single phases either disordered fluorite or ordered structure. An order-disorder transition (ODT) is evident changing composition, accompanied reduction in thermal conductivity (k). In comparison the ODT criteria developed from ternary oxides, these are more prone to disorder, but still controlled similar factors (but at thresholds). Interestingly, there abrupt increases Young's modulus (E) low concentrations near both endmembers. The E/k ratios increased, suggests new route tailor ceramics via controlling cation ordering vs. disordering.