Phase Equilibria of the Yb2O3-MgO-SiO2 System at 1600°C and Implications for Environmental Barrier Coatings and Refractories

Understanding the phase equilibria of the Yb 2 O 3 -MgO-SiO 2 system is crucial to reveal the coating-medium interaction mechanism and guide composition design. In the present work, the isothermal section of the Yb 2 O 3 -MgO-SiO 2 system at 1600°C in air was systematically constructed using high-temperature equilibrium quenching experiment combined with XRD, SEM, and EPMA analyses. Ten phase regions were identified, including one liquid-phase region, four two-phase regions, and five three-phase regions. Comparative analysis with the binary subsystems highlights the restricted solubility of Yb 2 O 3 in MgO (1.61 wt%) and the associated asymmetry, which are rationalized by crystallographic constraints and defect energetics. This study fills a critical knowledge gap and provides essential phase equilibria data for designing advanced Yb-silicate coatings with enhanced CMAS and corrosion resistance, as well as for developing MgO-based refractory materials.