Electronic structure and the metal-semiconductor transition in BaPb1-xBixO3 studied by photoemission and x-ray-absorption spectroscopy

We have studied the electronic structure of BaPb 1-x Bi x O 3 and its changes across the composition-dependent metal-semiconductor transition using photoemission and O 1s x-ray-absorption spectroscopy. For the parent insulator BaBiO 3 , the peak-to-peak splitting of the Bi 6s band is found to be large, whereas, the minimum gap is much smaller, qualitatively consistent with the large (∼2 eV) optical gap of the direct type and the smaller (∼0.5 eV) transport gap of indirect type. Pb substitution for Bi induces new states of Pb 6s character outside the band gap of BaBiO 3 and does not induce in-gap spectral weight unlike in cuprate superconductors; the splitting of the Bi 6s band is not significantly reduced by Pb substitution throughout the semiconducting region