The crystallization behaviour of bismuth germanate glasses

Glassy samples containing Bi₂O₃ and GeO₂ in different ratios were prepared and absorption measurements were performed on the samples in the ultraviolet region in order to determine the optical behaviour. Thermal analysis performed on the vitreous samples gave the glass transition temperature and the crystallization temperature. The main crystalline phases separated during the heat treatment were Bi₄Ge₃O₁₂ (BGO) and Bi₂GeO₅. The activation energy of the crystallization process of the sample BGO (1∶3) was measured using the isothermal method, and the value obtained was 47.1 kcal mol⁻¹; the reaction order was equal to 1.1.