Structural investigation of bismuth borate glasses and crystalline phases

Glasses of the system: xBi(2)O(3)-(100-x)B2O3 (x = 20 to 66 mol%) were prepared and characterized by density, DSC, UV-visible absorption and B-11 MAS-NMR spectroscopy. Glass molar volume increases while the glass transition temperature decreases with Bi2O3 concentration. Densities of some bismuth borate glasses are found to be greater or very close to those of single crystal phases with equal composition. B-11 MAS-NMR studies determined that the fraction of tetrahedrally coordinated borons (N-4) is maximum at 42 mol% of Bi2O3 and that there is a local maxima in N-4 at Bi2O3 concentration of 50 mol%. Glasses containing Bi2O3 concentration of 33 mol% and higher show an unusual, intense absorption band just below the optical band gap. Two crystalline phases: Bi3B5O12 and Bi4B2O9 were prepared by devitrification of glasses and characterized by X-ray diffraction, FTIR and B-11 MAS-NMR studies. Both crystalline phases contained significantly lower N-4 than glasses with equal composition. (C) 2008 Elsevier B.V. All rights reserved.