Abstract
The optical property of Li2O-Al2O3-SiO2 glass-ceramic, with a near-zero thermal expansion coefficient, crystallized under high pressure has been studied. A hydrostatic pressure of 196 MPa was applied by a hot isostatic pressing (HIP) technique during the nucleation process and the crystal growth process. The temperature coefficient of the optical path length, 1/l•dS/dT, decreased by 0.6×10-6 K-1, because the temperature coefficient of the refractive index, dn/dT, was decreased by the HIP treatment. The decrease in dn/dT was ascribed to the suppression of the temperature coefficient of the molar polarizability, φ, of the glass-ceramic crystallized by the HIP treatment. It was concluded that the suppression of φ occurs in the crystalline phase during the HIP treatment, based on the fact that the reduced 1/l•dS/dT was maintained even after the relaxation of the densified structure in the glass phase upon thermal annealing. The decrease in the number of lattice defects in the crystalline phase was hypothesized to be a cause of the reduced φ.
