Structure of partially reduced xPbO (1-x)SiO2 glasses: combined EXAFS and MD study

We have studied the structure of partially reduced lead-silicate glasses using combined EXAFS (extended X-ray absorption fine structure) and MD (molecular dynamics) methods. The analysis was performed for glasses of x[(l - p)Pb pPbO] (I - X)SiO2 composition, x = 0.3,0.5,0.7, where parameter (I - p) describes the degree of reduction, i.e. the content of the granular metallic phase, appearing as the result of the reduction process (e.g. annealing in hydrogen atmosphere). In the EXAFS experiment (1 - p) was expressed via the time of reduction realized at 400 degrees C (1.5 It, 24 It, 70 h), whereas in the MD simulations it was determined precisely by using proper numbers of particles (corresponding to (1 - p) = 0.0, 0.25, 0.5, 0.75 and 1.0). In the paper we describe in detail the local structure around lead atoms and its changes in the function of glass composition and reduction degree. The tendency for agglomeration of Pb-0 into clusters, the formation of the granular metallic phase, and continuity of silica and lead oxide subnetworks are discussed. A good agreement between EXAFS-extractcd and MD-extracted parameters of the short-range structure encouraged us to preform a medium-range order analysis, based on the MD simulations only. Moreover, combining the EXAFS and MD methods we could correlate the reduction time (technological parameter) with the degree of reduction (I - p) and the actual state of the granular structure. The latter relation may be useful for controlled production of reduced glasses of pre-requested physical properties. (c) 2005 Elsevier B.V. All rights reserved.