Structural and High-Temperature Sintering Behavior of Fluorite–Pyrochlore Dual-Phase Rare Earth Zirconates

Abstract This study explores the synthesis and structural characteristics of pristine and doped La 2 Zr 2 O 7 and Gd 2 Zr 2 O 7 with a focus on their sintering behavior. The pristine La 2 Zr 2 O 7 was found to stabilize in defect pyrochlore structure, which evolves toward a more ordered pyrochlore structure upon high-temperature sintering, evidenced by the appearance and sharpening of superlattice reflections with increasing temperature. The (La₀.₈Gd₀.₂)₂Zr₂O₇ sample exhibited a similar behavior; however, the ordering process is sluggish due to the presence of Gd 3 ⁺ ions. In contrast, the Gd 2 Zr 2 O 7 and (La₀.₂Gd₀.₈)₂Zr₂O₇ samples were stabilized in a dual-phase structure with dominant defect fluorite structure with microdomains of pyrochlore as shown through XRD and Raman analysis. All the sintered samples displayed a stable microstructure; however, relatively finer nanocrystalline grains are observed in dual-phase Gd 2 Zr 2 O 7 and (La 0.2 Gd 0.8 ) 2 Zr 2 O 7 samples. The combined influence of disorder-driven resistance offered by the fluorite phase and grain boundary pinning by the pyrochlore phase renders these systems highly suitable for applications demanding thermal stability and preservation of microstructural features.