Crystallization Behaviour and Nanostructuring in Alkali Niobiosilicate Glasses

摘要

23K2O·27Nb2O5·50SiO 2(KNS),13K2O·10Na2O·27Nb2O5·50SiO 2(KNaNS) and 15K2O·12Li2O·27Nb2O5·46SiO2(KLiNS) transparent glasses were synthesized by melt-quenching technique,and studied by differential thermal analysis(DTA),X-ray diffraction(XRD) and high-resolution transmission electron microscopy(HRTEM) to reveal the effect of the devitrification behaviour on transparent nanostructure.Just above the glass transition temperature T g in the KNS glass,an unidentified phase was formed,while in KNaNS and KLiNS,mixed-alkali niobate phases with tungsten bronze structure were obtained by bulk crystallization.Heat treatments at T g performed on the KNS glass resulted in the transparent nanostructure with second order harmonic generation(SHG) activity.Heat treatment for 10 h on KNaNS and KLiNS decreased the first DTA exothermic peaks(at least 24C),indicating the bulk nucleation,which was confirmed by the DTA in comparison with the powdered as-quenched samples.KNaNS and KLiNS showed similar XRD profiles as the K3Li2Nb5O15 crystal with the five most intense peaks at 22.7,29.4,32.3,46.3 and 52.0 deg.HRTEM micrograph showed clear-cut nano-sized circular domains and spherical nanocrystals dispersed into the amorphous matrix.