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 (Tg) 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.