EXAFS spectroscopic study of PbO-Bi2O3-Ga2O3 glasses

Extended X-ray absorption fine structure (EXAFS) spectra for ternary heavy metal oxide glasses with compositions of (1 - x)(0.75PbO + 0.25Ga(2)O(3)) + xBi(2)O(3) where x increased from 0 to 0.4 in 0.1 increments, indicate the formation of GaO4 tetrahedral unit with Ga-O bond length of similar to 1.87 A in all glasses. Pb also forms both PbO3 and PbO4 polyhedra, but the average oxygen coordination number around lead decreases from 3.50 to 2.96 with decreasing PbO concentration. From the EXAFS data we conclude that Bi forms BiO5 and BiO6 units as it does in the alpha-Bi2O3 crystal. Two distinct Bi-O distances of similar to 2.18 and similar to 2.46 A were resolved. Formation of each type of the polyhedra results in shortage of total oxygen ions for forming two-fold coordinated oxygens and as a result, formation of three-coordinated oxygens becomes necessary. (C) 1999 Elsevier Science B.V. All rights reserved.