Phase Equilibria of the Yb 2 O 3 ‐MgO‐SiO 2 System at 1600°C and Implications for Environmental Barrier Coatings and Refractories

ABSTRACT 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.