The formation of strontium fluoride nano crystals from a phase separated silicate glass

The crystallization of nano crystalline rare earth or alkaline earth fluorides is of high importance for optically transparent partially crystalline materials. In this study, nano crystalline SrF2 is precipitated. In contrast to recently studied glass systems which allow the crystallization of alkaline earth fluorides, droplet phase separation is the initial step of the SrF2 crystallization. The large difference in the atomic number of strontium in comparison with the other glass components enables structural studies using electron microscopy. In a glass with the mol% composition 3.7Al2O3/12.3SrO/5.3K2O/8.0Na2O/60.3SiO2/10.4SrF2 nano crystalline SrF2 is formed after annealing the glass samples at temperatures in the range from 520 to 600 °C for 2 to 160 h. The size of SrF2 nano crystals remains constant within the limits of error and does neither depend on time nor on temperature. A highly viscous layer enriched in SiO2 is formed during crystallization hindering further crystal growth.