Glasses and their crystallization in the (1 − х)KNbO 3· хSiO 2 system at low glass-forming oxide contents, 0 ⩽ х ⩽ 0.35

Abstract

Glasses based on the K 2O–Nb 2O 5–SiO 2 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 SiO 2 or B 2O 3. In the present work, we studied glass-forming and crystallization properties of (1 − х)KNbO 3· xSiO 2 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 K 4Nb 6O 17 phase and a small amount of ferroelectric KNbO 3, along with ceolite-like, cristobalite and α-quartz SiO 2 phases precipitate at low temperatures in the range between the glass transition point, T g, and the first exothermic peak on DTA curve, whereas ferroelectric KNbO 3 precipitates at temperatures above 800 °C. Ferroelectric crystals which precipitate in the glass bulk are shown to produce high SHG activity.