Effect of Heat Treatment of Molten Bi 2 O 3 Containing 22 mol % SiO 2 on the State of the Metastable δ*-Phase Forming during Solidification

— We have studied the effect of isothermal holding of a melt containing 78 mol % Bi 2 O 3 and 22 mol % SiO 2 and various melt cooling schedules on the morphology, microstructure, and phase composition of crystals of a metastable solid solution based on the high-temperature δ-polymorph of Bi 2 O 3 (δ*-phase). The results demonstrate that high-temperature holding is favorable for melt supercooling and crystallization of the δ*-phase in a wide range of cooling rates. We have investigated peritectoid decomposition of the δ*-phase at subsolidus temperatures. Its products are a silicon dioxide-deficient δ 4 -phase and crystalline polymorphs of metastable SiO 2 .