Crystallization Behavior of Potassium Niobium Silicate Glasses

Crystallization behavior of potassium niobium silicate (KNS) glasses having compositions expressed by the general formula x K 2 O· x Nb 2 O 5 ·(1 ‐ 2 x )SiO 2 , with x = 0.167, 0.182, 0.200, 0.220, and 0.250, has been studied by DTA, X‐ray diffraction, second harmonic optical generation (SHG), and electron microscopy. Bulk crystallization of potassium niobates in glasses with compositions near K 2 O·Nb 2 O 5 ·2SiO 2 , as well as surface crystallization of KNbSi 2 O 7 phase, has been established. Transparent glass‐ceramics, based on potassium niobates with remarkable SHG signal values, can be obtained from glasses with the lowest silica content, by heat treatment at temperatures just above T g , while at higher temperatures from all of the glasses under investigation the main crystallizing phase is KNbSi 2 O 7 ferroelectric. Applying a dc electric field, grain‐oriented crystallization is produced in KNS glasses with development of significantly anisotropic arrangements of KNbSi 2 O 7 crystallites.