Thermal and optical properties of glasses of the system Bi2O3 – B2O3

In the binary system Bi₂O₃ – B₂O₃ glasses were prepared in the composition range 57.5 mol% ‐ 80 mol% B₂O₃ by defined slow cooling of large melt samples (about 75 cm³, each). Temperatures of crystallization, of melting and of glass transition were determined and density data of the glasses were derived using the hydrostatic weighting method. Thermal expansion coefficients and high precision refractive indices, together with their dispersion, were measured. The measured physical properties indicate subtle discontinuous structural changes of the glasses with glass composition, that match with the ranges of existence of the crystalline compounds of the binary system Bi₂O₃ – B₂O₃. Thermal investigations together with X‐ray powder diffraction analyses of crystallized glass samples prove the so far doubtful existence of a borate compound named “BiBO₃” in the PDF within the composition range 52.5 – 57.5 mol% B₂O₃.