Variation of the transmittance and the Kerr constant during the crystallization of sodium-niobium-silicate glasses

摘要

This paper discusses the interconnection of the structure of sodium-niobium-silicate glasses, heat-treated isothermally in the temperature interval 660-700 degrees C for various times, with their extinction coefficient and Kerr constant. A spinodal phase separation occurs during heat treatment, followed by precipitation of a nano-size crystalline phase of sodium niobate. The volume increase of the crystalline phase is associated with nucleation of the crystals during the entire period of crystallization, whereas the size of the crystals remains virtually constant. The extinction coefficient substantially decreases toward the end of the crystallization stage as a consequence of interference effects in the scattering, caused by ordering elements in the relative position of the crystals. A model is proposed to describe how the extinction coefficient depends on the degree of crystallinity and the wavelength of the light. The dependence of the Kerr constant on the volume fraction of the crystalline phase is well described in terms of the effective-medium approximation. (C) 2006 Optical Society of America.