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.