Experimental and theoretical study of the electronic structures of alpha-PbO and beta-PbO2

The electronic structures of alpha-PbO and beta-PbO2 have been investigated by X-ray photoemission, X-ray absorption and X-ray emission spectroscopies, supported by bandstructure calculations performed within the framework of density functional theory. The relative intensity of a peak found at the bottom of the valence band for both oxides changes dramatically between Al K alpha X-ray photoemission and O K shell X-ray emission spectra, demonstrating that the states associated with this peak possess dominant Pb 6s character. This finding is in accord with partial densities of states derived from bandstructure calculations but is at variance with the conventional view that the Pb 6s states in PbO are close to the Fermi energy and hybridise with empty 6p states to give a metal based directional 6s - 6p lone pair. The photoemission onset of beta-PbO2 contains a well-defined metallic Fermi edge. The position of the onset structure suggests that the metallic nature of PbO2 arises from occupation of conduction band states above the main valence band, probably arising from oxygen vacancy defects. The conduction electrons of beta-PbO2 are strongly perturbed by ionisation of Pb core levels, giving rise to distinctive satellites in core XPS whose energies correspond to those of the conduction electron plasmon.