fig11

Figure 11. Schematic diagram of the cP4 to hR20 polymorphic transformation mechanism. (A) Distribution of closely packed plane atoms in the two-structured Al₃Er phases; (B) Initial state (t₁) and the three transformation stages (t₂-t₄) of microstructure evolution during polymorphic transformation. t₁: Initial formation of cP4-structured Al₃Er phase; t₂: Isolated nucleation of the hR20-structured Al₃Er phase on phase boundaries of cP4-structured Al₃Er phase; t₃: Autocatalytic nucleation and growth dimensionality transition of hR20-structured Al₃Er phase; t₄: Formation of polycrystalline hR20-structured Al₃Er.