Phase Composition and Microstructure of Crystallization Products of Molten Bi2O3 ⋅ GeO2 under Various Cooling Conditions

Abstract

We have studied the influence of melt heat treatment, initial cooling temperature (t_cooling 0), and cooling schedule for a melt containing 50 mol % Bi₂O₃ and 50 mol % GeO₂ on the phase composition, macrostructure, and microstructure of crystallizing solid phases. According to X-ray diffraction, optical microscopy, and scanning electron microscopy data, the phase composition of the crystallization products is represented by either the metastable bismuth germanate Bi₂GeO₅ or a mixture of metastable and stable phases, depending on melt cooling conditions. The crystallization behavior of phase-pure Bi₂GeO₅ under identical cooling conditions has been shown to be influenced by not only t_cooling 0 but also isothermal preholding of the melt for 1 h at a temperature of 1160°C.