Pb L3 EXAFS and near-edge studies of lead metal and lead oxides

Abstract

The Pb L 3 extended X-ray absorption fine structure (EXAFS) spectra of polycrystalline foil and powder specimens of Pb metal; polycrystalline PbO 2, and both red and yellow allotropes of PbO have been recorded. Although the EXAFS oscillations in the spectrum of Pb metal are rapidly damped with increasing temperature, they are easily detected, contrary to recent suggestions (Samant et al., J. Am. chem. Soc. 109, 5970, 1987) that the large thermal motion in Pb completely damps the EXAFS signal at room temperature. We suggest that Samant et al. may have failed to observe EXAFS because of large structural disorder in their sample. There are indications that anharmonicity of thermal motion affects the EXAFS signal since, with the standard EXAFS analysis, there is an apparent decrease in the nearest neighbour (NN) Pb-Pb distance of metallic Pb with increased temperature. The near-edge and EXAFS signals of the PB oxides are analysed. As expected from their much more rigid ionic structure the Pb L 3 EXAFS of the lead oxides is not greatly changed between 77 and 300 K.