Abstract: Rare earth silicates (RE₂SiO₅) are the focus of the new-generation environmental barrier coatings (Environmental Barrier Coatings, EBCs) materials due to their excellent environmental resistance, among which Yb₂SiO₅ exhibits particularly outstanding overall performance. However, the controlled synthesis of high-quality nano-powders remains a bottleneck limiting coating performance enhancement. In this study, Yb₂SiO₅ nano-powders were synthesized via a cocurrent coprecipitation-calcination method. The effects of Yb/Si molar ratio, calcination temperature, and calcination time on phase composition, crystallite size, and morphological evolution were systematically investigated, and the underlying mechanisms governing powder synthesis were elucidated. The results show that a Si-rich environment can lower the crystallization temperature from 1046.6 ℃ to 1006.5 ℃ and significantly reduce the X1→X2 phase transition temperature. The low-temperature phase X1-Yb₂SiO₅ exhibits a lamellar structure (100~200 nm), whereas the high-temperature phase X2-Yb₂SiO₅ consists of uniform, irregularly granular nanoscale powders (<100 nm). In the calcination temperature range from 800 ℃ to 1200 ℃, the amorphous precursor firstly transforms into lamellar low-temperature phase X1-Yb₂SiO₅ crystals; subsequently, X2-Yb₂SiO₅ nuclei precipitate and grow on the surface, eventually developing into irregular granular X2-Yb₂SiO₅ particles, thereby completing the X1-Yb₂SiO₅→X2-Yb₂SiO₅ (X1→X2) phase transition. Deviations of the Yb/Si molar ratio from the stoichiometric ratio lead to the precipitation of impurity phases, such as Yb₂O₃ (Si deficiency) or Yb₂Si₂O₇ (Si excess), the specific types of which are determined by the types of nuclei formed during calcination. The calcination time primarily affects the kinetics of phase transformation, prolonged cancination can lead to low-temperature sintering of the powder particles. This work provides a theoretical basis and experimental guidance for the controlled synthesis of high-performance rare-earth silicate nano-powders.

Key words: environmental barrier coating, ytterbium silicate, co-precipitation method, Yb/Si molar ratio, nano-powders