Optical and physical properties of bismuth borate glasses related to structure

We have investigated the optical and physical properties of bismuth borate 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 molar ratio of bismuth oxide to boron oxide In particular we related the density glass transition temperature and short wavelength optical cutoff to significant structural changes occurring in the glass as the composition was varied. We found that the maximum of the glass transition temperature coincides with the minimum in the boron oxide molar volume at around J=0.3. The glass transition also levelled off after) =3 indicating gentler steady changes of the structure The optical cutoff increased in wavelength as the bismuth concentration was increased and this effect was attributed to a shift to more covalent bismuth oxygen bonding (higher optical basicity).