Optical property and microstructure of LaO3/2-TiO2 glasses prepared by aerodynamic levitator

초록

Titanium oxide (TiO2) itself represents high refractive materials. To fabricate TiO2 based glasses with a high refractive index, it is required to make glass with multi-component system by incorporating a high packing density component such as BaO, La2O3. Iwasaki et al. studied La2O3-TiO2-SiO2 glass derived from a sol-gel process for high refractive index glass (Iwasaki et al. 2007). Maximum refractive index of the glass was just 1.64 at 10La2O3-10TiO2-80SiO2 composition. It is usually difficult to vitrify TiO2 without adding network former or modifier, thereby resulted in decrease in refractive index. Containerless melting technique can be an alternative processing route which produces a high refractive glass without adding glass former. Kaneko et al. successfully fabricated LaO3/2-TiO2 glass without adding SiO2 glass former via containerless melting method (Kaneko et al. 2012). They attained high refractive index of 2.29 at 31LaO3/2-69TiO2 composition. Kaneko et al. also investigated glass-forming region, glass transition temperature (Tg), crystallization onset temperature (Tx), and thermal stability (ΔT=Tx-Tg). They reported that transparent LaO3/2-TiO2 glasses were easily formed at near the eutectic point (~29.5 mol% LaO3/2) in LaO3/2-TiO2 binary phase diagram. However, the changes in local structure of glass with composition were not investigated in detail. The local structure should be studied to understand thermophysical/optical properties of glass. Therefore, in this study, LaO3/2-TiO2 glass was prepared by containerless aerodynamic levitation. The glass forming ability of LaO3/2-TiO2 binary system was investigated at wide composition range. The relationship between optical properties and microstructure was investigated and discussed based on the results obtained by high/room temperature XRD, DSC, SEM, and XAFS (X-ray absorption fluorescence spectroscopy).