Medium-Entropy Chromites (Nd/La)0.25RE0.25Gd0.25Y0.25CrO3 (RE = Pr, Er, Sm, Dy, or Nd): Synthesis, Crystal Structure, and Theoretical Analysis of Oxygen-Ion Migration.

Four-component medium-entropy chromites, (Nd/La)0.25RE0.25Gd0.25Y0.25CrO3 (RE = Pr, Er, Sm, Dy, or Nd), were synthesized via solution combustion. Whereas the Nd-based series formed single-phase orthorhombic perovskites (space group Pnma), their La-based analogues were multiphase. Both series exhibit a similar systematic composition-structure relationship, indicating that average structural parameters alone are insufficient to explain phase stability in medium-entropy chromites. BVSE analysis of oxygen-ion migration in the Nd-based compounds revealed a connected three-dimensional oxygen migration network with the lowest migration barrier (0.86 eV) for Nd0.25Er0.25Gd0.25Y0.25CrO3. Comparison with the corresponding ordered RECrO3 compounds shows that the variation of the calculated migration barriers is significantly smaller in the medium-entropy compositions, while the same compositional trend is preserved.