Glasses and their crystallization in the (1 − х)KNbO3·хSiO2 system at low glass-forming oxide contents, 0 ⩽ х ⩽ 0.35

Glasses based on the K2O–Nb2O5–SiO2 system have been a subject of numerous studies thanks to promising electro-optical and non-linear optical properties. Most of the studies of Nb-containing glasses deal with compositions including not less than 40 mol% of SiO2 or B2O3. In the present work, we studied glass-forming and crystallization properties of (1 − х)KNbO3·xSiO2 glasses with x varying from 0 to 35 mol% by melt quenching between steel plates or by exposure to air or nitrogen flow. Thin transparent glassy plates can be obtained by quenching via pressing between metal plates for glasses with x ⩾ 0.12, and transparent glass-ceramics allowing a remarkable second harmonic generation (SHG) response can be formed by heat-treatment near the first exothermic differential thermal analysis (DTA) peak over a wide range of glass compositions. It is shown that in these glasses, the crystalline K4Nb6O17 phase and a small amount of ferroelectric KNbO3, along with ceolite-like, cristobalite and α-quartz SiO2 phases precipitate at low temperatures in the range between the glass transition point, Tg, and the first exothermic peak on DTA curve, whereas ferroelectric KNbO3 precipitates at temperatures above 800 °C. Ferroelectric crystals which precipitate in the glass bulk are shown to produce high SHG activity.