CRYSTALLIZATION STUDY OF HEAVY-METAL FLUORIDE GLASSES ZBLAN BY RAMAN-SPECTROSCOPY

Heavy metal fluoride glass ZBLAN, with molar composition ZrF4(53)-BaF2 (20)-LaF3(4)-AlF3(3)-NaF(20), was studied in vacuum at high temperatur es up to 480 degrees C by Raman spectroscopy, The vitreous glass was f ound to crystallize at 330 degrees C, most probably to beta-BaZrF6 cry stallites, High-temperature experiments in air were also carried out a nd ZrO2 was formed at the surface of the sample. Doping by SiO2 increa ses the crystallization temperature by 25 degrees C for experiments pe rformed in air, while PbO2 dopants are found to react with the host. ( C) 1997 John Wiley & Sons, Ltd.