Phase separation in yttrium silicate glass prepared by the sol–gel method

Yb2O3–10Y2O3–89SiO2 (mol%) glass was prepared by the sol–gel method. The phase evolution of the glass as a result of heat treatment was investigated. When heat-treated at 700 °C, phase separation, i.e. a spherical amorphous phase enriched with Y3+ and Yb3+ distributed separately among the glassy matrix, was observed by TEM. The immiscibility boundary of the system was determined to be between 1350 and 1400 °C. The activation energy of phase separation was evaluated to be 347 kJ/mol through non-isothermal experiments. When heated at 1150 °C for 4 h, nano-sized α-Y2Si2O7 and cristobalite crystallites were precipitated from the spherical and matrix glassy phases, respectively.