Vol. 33, Issue 1, pp. 161-166

Abstract

Crystallization of LaF₃ in glasses from the SiO_2–Al₂O_3–Na₂O–LaF₃ system has been investigated. The structure of this compound makes it a good host for the rare earths. It has been found that the range of chemical compositions of glasses from which ultra-transparent glass-ceramics with LaF₃ nanocrystallites can be obtained is very limited. It is determined by crystalochemical factors, in particular by the position of Al and La in the glass structure. The optical proportions between Al₂O₃, Na₂O and LaF₃, leading to the effect of nanocrystallization of this fluoride, as well as the temperature and time of ceramization, have been determined. If these proportions are not maintained, the undesirable crystals of nepheline (NaAlSiO₄) and LaAl₂O₃ are formed. It has been found that the crystallization of LaF₃ is essentially affected by the kind of the compounds used to introduce La and F into the glass. In the obtained material the dimensions of LaF₃ crystallites varied from 20 to 100 nm.