Fabrication of Crystallized Glasses with Nanocrystal Orientation by Heat Treatment in External Fields

Abstract

Nanostructures are the gateway into a realm in physical, chemical, biological and materials science. In particular, optically transparent nanostructured materials showing optical nonlinearity or ferroelectricity have received much attention, because such materials have a high potential for applications in photonic devices such as optical switching. Crystallization of glass is one of the effective methods for fabrication of nanostructures, and many studies on crystallized glasses consisting of nanocrystals have been carried out. It is also of importance to develop techniques for enhancing optical properties of nanocrystallized glasses. In this study, we applied a high magnetic field of 10 T in the crystallization of the BaO-TiO₂-SiO₂ glass and examined whether the application of such a high magnetic field has the effect on the second-order optical nonlinearity of Ba₂TiSi₂O₈ nanocrystals. We also examined the effect of thermal poling on the second harmonic intensity of transparent nanocrystallized glasses consisting of Ba₂TiSi₂O₈ nanocrystals. It was clarified that the formation of Ba₂TiSi₂O₈ nanocrystals is depressed in the crystallization under 10T and the c-axis orientation of nanocrystals occurs along to the applied magnetic field. The prominent enhancement in the second harmonic (SH) intensity is observed due to the thermal poling (DC electric voltage: 8.8kV/cm, temperature: 110～300℃，time: 1 h), demonstrating that a thermal poling is an effective method in enhancing anisotropic polarization of ferroelectric Ba₂TiSi₂O₈ nanocrystals in the crystallized glasses. The present study proposes that the Maker fringe pattern for the SH intensity of nanocrystallized glasses is very sensitive to the anisotropic polarization of nanocrystals at the surface.