Compositional effects on the optical and thermal properties of sodium borophosphate glasses

A series of sodium borophosphate glasses of the composition (1−x)NaPO₃−xB₂O₃ have been synthesised from Na₂CO₃, B₂O₃ and P₂O₅ and their optical and thermal properties investigated. The results show that refractive index (n) and glass transition temperature (T_g) show a maximum at about B/(B+P)=0.6 while thermal expansion coefficient (α) and thermo-optic coefficient (dn/dT) change monotonically with the B/(B+P) ratio. These observations can be interpreted based on the incorporation of BO₃ and BO₄ units into the glass structural network.