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, phi, and the thermal expansion coefficient, alpha. The dS/dT value of 2.6 mol% B2O3-doped glass-ceramic was 12.5 x 10(-6)/degrees C, which was 0.9 x 10(-6)/degrees 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 phi. The reduction in phi from B2O3 doping was probably attributable to numerical reduction in non-bridging oxide ions with larger phi 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 beta-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B2O3-doped glass-ceramic crystallized under 196 MPa was 11.7 x 10(-6)/degrees C. That value was slightly larger than that of silica glass. The a value of this glass-ceramic was smaller than that of silica glass. (C) 2008 Elsevier B.V. All rights reserved.