In this study, a series of (LaxYb1-x)2Zr2O7 powders with \(0\le x\le 1\) were synthesized by a co-precipitation method to investigate the effect of rare earth (RE) site substitution (La3⁺ and Yb3⁺) on phase stability, structural disorder, and high-temperature sintering behavior for thermal barrier coating (TBC) applications. The synthesized powders were characterized using TG/DTA, XRD, Raman spectroscopy, FTIR, FESEM, and EDS before and after calcination at 1000 and 1300 °C, as well as after prolonged heat treatment at 1300 °C for up to 50 h. The results showed a clear composition-dependent transition from ordered pyrochlore in La-rich samples to defect fluorite in Yb-rich samples, while intermediate compositions exhibited mixed-phase behavior and peak broadening associated with increased lattice disorder. Raman and XRD analyses confirmed that prolonged heat treatment improved crystallinity and promoted phase ordering in La-rich compositions, whereas Yb-rich compositions retained predominantly defect fluorite character. FESEM observations revealed noticeable grain growth after calcination and heat treatment, with La-rich compositions showing better resistance to coarsening than Yb-rich ones. Overall, the La–Yb zirconate system demonstrates that compositional tuning at the RE site is an effective strategy for balancing phase stability and sintering resistance in advanced TBC materials.
