Preparation and characterization of quenched KNbO₃-Nb₂O₅ glass

Abstract

KNbO₃-Nb₂O₅ glasses were prepared with molar ratio of K/(K + Nb) from 0.16 to 0.5 by using a twin-roller quenching apparatus. Most KNbO₃-Nb₂O₅ glasses crystallized to stable phases such as KNbO₃, K₂Nb₄O₁₁, K₃Nb₇O₁₉, KNb₃O₈ and K₂Nb₈O₂₁ via metastable phases after heat treatment and K₄Nb₆O₁₇ glass directly crystallized to K₄Nb₆O₁₇ crystal. KNbO₃ glass consisted of the corner-shared NbO₆ octahedra, while the amounts of the edge-shared NbO₆ octahedra in the KNbO₃-Nb₂O₅ glass structure increased with decreasing K⁺ ion content. The band gap energies and the ionic conductivity of the KNbO₃-Nb₂O₅ glasses increased with increasing K⁺ ion content, but the density and the activation energy of the ionic conduction decreased. The glasses possessed high dielectric constants appfoaching those of ferroelectric crystals at high temperature around the crystallization temperature. The dielectric constants of the glasses, however decreased greatly with decreasing temperature and with increasing frequency.