OPTICAL AND PHYSICAL-PROPERTIES OF BISMUTH BORATE GLASSES RELATED TO STRUCTURE

We have investigated the optical and physical properties of bismuth bo rate glasses over wide compositions ranging from 0 to 88 mol% bismuth oxide. This corresponds to the range J=0 to J=7.5, where J is the mola r ratio of bismuth oxide to boron oxide. In particular we related the density, glass transition temperature and short wavelength optical cut off to significant structural changes occurring in the glass as the co mposition was varied. We found that the maximum of glass transition te mperature coincides with the minimum in the boron oxide molar volume a t around J=0.3. The glass transition also levelled off after J=3 indic ating gentler steady changes of the structure. The optical cutoff incr eased in wavelength as the bismuth concentration was increased and thi s effect was attributed to a shift to more covalent bismuth oxygen bon ding (higher optical basicity).