Achieving a high ionic conductivity in Bi2O3-based high-entropy ceramics

Bi 2 O 3 -based high-entropy ceramics of (Bi 1-x (Y 0.2 Er 0.2 Zr 0.2 Gd 0.2 Dy 0.2 ) x ) 2 O 3±δ ((Bi 1-x (YEZGD) x ) 2 O 3±δ , x = 0.1, 0.15, 0.2 and 0.3) were synthesized via solid-state reaction method combined with conventional sintering (in 850–930 °C for 10 h). The samples of (Bi 1-x (YEZGD) x ) 2 O 3±δ (x = 0.15, 0.2, and 0.3) possess a fluorite-structured phase (δ-phase), while 18.50 wt% tetragonal β-phase coexists with the δ-phase in (Bi 0.9 (YEZGD) 0.1 ) 2 O 3 . All samples exhibit a uniform elemental distribution and a high relative density of 93.01–96.57 %. Among all compositions, (Bi 0.8 (YEZGD) 0.2 ) 2 O 3±δ demonstrates the highest ionic conductivity (1.32 × 10 −4 –1.09 × 10 −1  S/cm in 300–550 °C), approximately 5.7 times higher than that of the single-doped Bi 2 O 3 -based ceramic of (Bi 0.8 Er 0.2 ) 2 O 3 at 500  ° C. This enhancement is mainly attributed to the random distribution of multiple cations with various ionic radii, which induces lattice distortions that suppress dopant clustering and enhance oxygen vacancy mobility. The results suggest that the high-entropy design offers an effective strategy for improving the ionic conductivity of Bi 2 O 3 -based electrolyte at medium-low temperatures.