Network structure of B2O3-PbO and B2O3-PbO-PbBr2 glasses analyzed by pulsed neutron diffraction and Raman spectroscopy

The structure of (1 - x)B2O3-xPbO (x = 0.20, 0.30, 0.40) glasses and (0.98 - x)B2O3-xPbO-0.02PbBr(2) (x = 0.18, 0.28, 0.38) glasses was studied by time-of-flight pulsed neutron diffraction. The structural parameters for each atomic pair were optimized in the Q-space, and the distances of the near neighbor B-O correlations forming trigonal-plane BO3 units and tetrahedral BO4 units in boroxol-like rings were estimated at 0.137 and 0.148 nm, respectively. The existence of the species was also supported by Raman spectroscopy and ab initio molecular orbital calculation. The Pb atoms served as modifiers to hold the networks, the neighboring oxygens among which formed distorted octahedra. The distances of Pb-O pairs were divided into two groups of approximately 0.25 and 0.30 nm, respectively. The medium-range order derived from Pb atoms was recognized in the structure factor S(Q) over the composition range of this work. The short-range order in the boron-oxygen network was unaffected by PbBr2 doping, but Br- ions were coordinated in the oxygen sites around Ph atoms. (C) 2004 Elsevier B.V. All rights reserved.