XAFS study on the local order of Pb in PbO borate glasses

Abstract

An XAFS study on several samples of borate glasses with increasing PbO concentrations was performed in order to detect a possible clustering of Pb atoms or PbO structures. Samples with concentrations from 28.6 up to 75% of PbO were examined at the L-3 edge of Pb. Analysis of data was carried out by experimental comparison with low temperature crystalline references and with the results of theoretical evaluation of amplitude and phases of possible Pb-Pb and Pb-O structures. It was observed that, even at the highest concentration, metallic Pb segregation is incompatible with the obtained XAFS spectra. The most probable structure of Pb neighbours is a tetrahedral replica of the PbO structure (litharge or red PbO). This order weakly extends also to second neighbours, except for the least concentrated sample in which only a distorted first PbO shell was reproduced