Studies of glass structure in the system Bi2O3-B2O3-SiO2

The structure of single-phase glass in the Bi2O3-B2O3-SiO2 system has been investigated by the method of large angle X-ray scattering (LAXS). The glass of two-component systems Bi2O3-B2O3 and Bi2O3-SiO2 and those of compositions in three sections with the Bi2O3 content varying from 20 to 80 mol % at B2O3: SiO2 ratios equal to 3, 1, and 1/3 have been studied. The LAXS data indicate the existence of the structural ordering beyond the first coordination spheres in glass of the Bi2O3-B2O3-SiO2 system. Three clearly expressed diffraction maxima on LAXS angle dependences are caused by the presence of repeating interatom distances in the structure of the short- and intermediate-range order. This results from the formation of structural groups with the participation of modifier ions and, consequently, ordering in the boron-silica surrounding of the bismuth ions. A partial crystallization is observed on the cooling of the melts containing 50% Bi2O3 in the Bi2O3-SiO2 system and 80% Bi2O3 in the Bi2O3-B2O3 system. The area of liquid phase separation is formed at the Bi2O3 content of less than 30 %. The structure of the glass under study corresponds to the model of associated ideal solutions, which is a partial case of the generalized lattice theory of associated solutions.