Phase Evolution and Compositional Homogenization in Mechanochemically Activated High‐Entropy Manganite Perovskites

ABSTRACT

The synthesis of single‐phase La _0.35 Gd _0.35 Ca _0.3 (Mn _0.5 Co _0.1 Cu _0.1 Fe _0.1 Ni _0.1 Mg _0.1 )O ₃ high‐entropy perovskite oxides was investigated using mechanochemical activation followed by thermal treatments. The influence of milling time (1–150 h) and post‐milling annealing temperature on phase formation, compositional homogeneity, and structural evolution was systematically analyzed. It was found that high‐energy milling alone was not sufficient to fully incorporate all oxide precursors into the perovskite lattice, even after prolonged milling times. Subsequent thermal treatments were therefore required to achieve compositional homogeneity and to stabilize the perovskite structure. Although thermal treatments improved elemental uniformity, they also promoted the precipitation of secondary phases depending on the prior milling duration. Fully homogeneous single‐phase materials were only obtained after milling for 30 h followed by annealing at 1473 K, while longer milling treatments yielded precipitation of new phases during annealing. Thus, the processing window leading to the formation of a pure and homogeneous high‐entropy phase is narrow and requires careful optimization of both mechanochemical and thermal treatment conditions.