Compositional effects on the thermo-optic coefficients of barium borophosphate glasses

Two series of ternary glasses with compositions of 0.5BaO-xB(2)O(3)-(0.5-x)P2O5 (Series 1) and (1-x)Ba(PO3)(2)-xB(2)O(3) (Series 2) have been prepared. Various properties, such as refractive index (n), glass transition temperature (T-g), thermal expansion coefficient (alpha) and thermo-optic coefficient (dn/dT) have been measured to assess the potential of these borophosphate glasses for athermalisation. The results obtained for these glasses can be explained based on the incorporation of BO3 and BO4 units into the glass structural network. To achieve athermalisation, a negative dn/dT is required to counter the effect of thermal expansion.