Glass formation and some physical properties in NaPO3 – LiF and NaPO3 – (0.4 AlF3 – 0.6 CaF2) systems

The area of glass formation in NaPO₃–LiF–(0.4AlF₃ – 0.6CaF₂) system was determined. The glasses were synthesized using standard melt-quenching techniques. The concentration dependencies of the glass transition temperature, refractive index, density, molar volume, microhardness, and crystallization products were obtained. In (NaPO₃)_100-x–(LiF)_x glass the linear decrease of noted parameters was observed. The LiF additives to the phosphate network caused the formation of a "friable" glass network. In (NaPO₃)_100-x –(0.4AlF₃ – 0.6CaF₂)_x system the concentration dependencies were more complex due to the formation of a mixed fluorophosphate network. It was assumed that the structural groups changed from metaphosphate (PO₃⁻)_n in the initial composition to the combinations of P(O,F)₄+[MeF₆]+[MeF₄] in the final stage. The microhardness values (>360 kg/mm²) of NaPO₃– (0.4AlF₃ – 0.6CaF₂) glasses with high fluoride content were comparable to lead silicate glasses, which indicates the possibility of their practical application in optical instrumentation and devices.