Study of the thermally stimulated glass structure reconstruction in extruded Li 2O · 2SiO 2 glasses by the method of radiation color center chronospectroscopy

Abstract

Longitudinal (LS) and transverse (TS) Li 2O · 2SiO 2 glass samples cut along and across the axis of cylindrical rods produced by means of extrusion were investigated. All the glasses contained iron impurities (∼80 ppm). Spectra of radiation induced absorption (RIA) and kinetic curves, Δ a( E)= f( t), where E is the energy of a band and t is time, of the RIA relaxation were measured in the LS and TS before and after their heat treatment at 465°C (∼5°C above the glass transition temperature, T g). It turned out that, at smallest irradiation doses, Fe 3+ ions capture free electrons excited by X-rays. As a result, intrinsic hole color centers (CCs) with absorption bands at 2.1, 2.8, and 3.9 eV and impurity electron CCs [radiation reduced ions (Fe 3+) −] are formed. Radiation induced conversion Fe 3+ → (Fe 3+) − causes negative RIA with the maximum at ∼5.7 eV. Centers (Fe 3+) − and intrinsic hole CCs do not participate in the process of mutual recombination. With a dose increase, intrinsic electron CCs are created with absorption band at ∼5.5 eV which compensate the above negative RIA. These CCs recombine with intrinsic hole CCs. Before the heat treatment, rates of CCs recombination decay for the LS and TS differ but they are approximately equal after annealing for 4 h. As these rates must depend on distances between recombining electron and hole CCs and these distances in axial and radial directions of extruded glasses appear to be different, we conclude that the heat treatment stimulates reconstruction of the extruded glass anisotropic structure to an isotropic state similar to that of a non-extruded glass.