Thermo-optic properties of B2O3 doped Li2O–Al2O3–SiO2 glass–ceramics

Reduction in the temperature coefficient of the optical path length, dS/dT of Li2O–Al2O3–SiO2 glass–ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ϕ, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B2O3-doped glass–ceramic was 12.5  × 10−6/°C, which was 0.9 ×  10−6/°C smaller than that of B2O3-free glass–ceramic. On the other hand, reduction in dS/dT through B2O3 doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass–ceramic through B2O3 doping is caused by the reduction in ϕ. The reduction in ϕ from B2O3 doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ϕ value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B2O3-doped glass–ceramic crystallized under 196 MPa was 11.7 ×  10−6/°C. That value was slightly larger than that of silica glass. The α value of this glass–ceramic was smaller than that of silica glass.