Development of rare earth doped oxyfluoride glass ceramics for photonic applications

Abstract

Glass ceramics are fine-grained polycrystalline materials produced when glasses of appropriate compositions are heat treated and thus undergo controlled crystallization to a lower energy crystalline state. A glass-ceramic is formed by the heat treatment of glass which results in crystallization. Crystallization of glasses is due to the thermodynamic drives for reducing the Gibbs free energy and the Amorphous Phase Separation (APS) which assists the crystallization process by easily producing a nucleated phase than it would in the original glass. A glass-ceramic is generally not fully crystalline; with the microstructure being 50 95 volume % crystalline with the rest being residual glass. When the glass undergoes heat treatment, one or more crystalline phases may form. Both the compositions of the crystalline and residual glass are different to the parent glass. newlineIn order to develop glass-ceramics that have desirable properties, it is vital to control the crystallization process so that an even distribution of crystals can be formed. This is done by controlling the nucleation and crystal growth rate. The nucleation rate and crystal growth rate has been shown to be a function of temperature and have been accurately measured experimentally. The crystallization process enhances the properties of glass-ceramics compared to the parent glass. The glass-ceramic formed depends on efficient internal nucleation from controlled crystallization which allows the development of fine, randomly oriented grains without voids, microcracks, or other porosity. This results in the glass-ceramic being much stronger, harder and more chemically stable than the parent glass. newline