Structure of low-silica glasses in the K2O-Nb2O5-SiO2 system

• Published in: Theoretical foundations of chemical engineering Vol. 47; no. 1; pp. 1 - 9
• Main Authors: Sarkisov, P. D., Paleari, A., Sigaev, V. N., Lotarev, S. V., Golubev, N. V., Stefanovich, S. Yu, Champagnon, B., Vouagner, D., Cusi, M., Fargin, E.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 2013
• Subjects: Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Small Angle Neutron Scattering; Initial Glass; CTHEORETICAL Foundation; JCPDS Database; Potassium Niobate
• ISSN: 0040-5795; 1608-3431
• DOI: 10.1134/S0040579513010065

The nanostructure and nonlinear optical properties of high-niobium glasses in the (1 − x )KNbO 3 - x SiO 2 system with an SiO 2 content x = 0.05–0.35 have been studied by small-angle neutron scattering (SANS), electron microscopy (EM), and second-optical-harmonic generation (SHG). Vitreous samples are manufactured by the methods of fast melt cooling (pressing with metal plates and quenching between rotating rolls). Glasses with x < 0.12 have been established to form a micro-inhomogeneous structure in the form of silica-enriched regions at the cooling rates used. According to SANS data, quenched glasses with x > 0.2 are homogeneous, but form a silica-enriched nanostructure after thermal treatments. At temperatures below ∼ T g + 50°C, silica-enriched regions manifest a very slight tendency to grow, whereas, according to SANS and X-ray diffraction data, their chemical composition is observed to shift appreciably towards SiO 2 with thermal treatment. The obtained data on an inhomogeneous structure allows us to clarify the complicated character of the previously revealed dependence T g ( x ). Nano-inhomogeneous transparent samples produce a weak SHG signal, which indicates the quasi-periodic modulation of the chemical composition and, correspondingly, polarizability, in the volume of glass. The nonlinear optical phase KNbO 3 precipitates at later stages of crystallization, when a glass loses its transparency. In this case, the SHG signal is amplified by several orders of magnitude.