Structural evolution and synthesis mechanism of dual-phase (La0.2Sm0.2Gd0.2Dy0.2Yb0.2)2Zr2O7 nanocomposite with excellent phase stability

A series of novel dual-phase medium-entropy (La 1/3 Gd 1/3 Yb 1/3 ) 2 Zr 2 O 7 , (La 0.25 Sm 0.25 Gd 0.25 Yb 0.25 ) 2 Zr 2 O 7 , (La 0.25 Gd 0.25 Dy 0.25 Yb 0.25 ) 2 Zr 2 O 7 and high-entropy (La 0.2 Sm 0.2 Gd 0.2 Dy 0.2 Yb 0.2 ) 2 Zr 2 O 7 (LSGDY) materials were designed and synthesized via an optimized chemical coprecipitation method. This study systematically investigates their precursor reaction pathways, structural evolution and resulting microstructure. Furthermore, the synthesis mechanism and high temperature phase stability of dual-phase high-entropy LSGDY were also discussed in detail. Results reveal that the precursor features a composite hydroxide structure with interconnected -[Zr-OH-Zr]-, -[Zr-OH-RE]- and -[RE-OH-RE]- chains, enabling atomic level cross-linking and mixing of RE and Zr elements. During the calcination process, the precursor initially transforms into a metastable fluorite phase nanocrystalline through dehydration and structural rearrangement, followed by further phase differentiation driven by the sequential cations and anions order. In contrast to medium-entropy systems, the synthesized LSGDY exhibits a unique dual-phase nanocomposite structure, where nanoscale pyrochlore phases are coherently embedded within a fluorite phase matrix, introducing significant dislocations and lattice distortions. The synergistic effect of preferential fluorite phase formation and high configurational entropy suppresses the long-range pyrochlore phase ordering, stabilizing the dual-phase nanocomposites. Furthermore, annealing tests at 1600 °C for 100 h confirm the excellent phase stability of LSGDY, demonstrating its great application potential for TBCs. This work not only elucidates the synthesis-structure correlations in dual-phase high-entropy zirconates, but also provides a new strategy for the property modulation of advanced high-entropy ceramics.