Nature of the band gap and origin of the conductivity of PbO(2) revealed by theory and experiment

Reference:

Scanlon, D. O., Kehoe, A. B., Watson, G. W., Jones, M. O., David, W. I. F., Payne, D. J., Egdell, R. G., Edwards, P. P. and Walsh, A., 2011. Nature of the band gap and origin of the conductivity of PbO(2) revealed by theory and experiment. Physical Review Letters, 107 (24), 246402.

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Official URL:

http://dx.doi.org/10.1103/PhysRevLett.107.246402

Abstract

Lead dioxide has been used for over a century in the lead-acid battery. Many fundamental questions concerning PbO(2) remain unanswered, principally: (i) is the bulk material a metal or a semiconductor, and (ii) what is the source of the high levels of conductivity? We calculate the electronic structure and defect physics of PbO(2), using a hybrid density functional, and show that it is an n-type semiconductor with a small indirect band gap of similar to 0.2 eV. The origin of electron carriers in the undoped material is found to be oxygen vacancies, which forms a donor state resonant in the conduction band. A dipole-forbidden band gap combined with a large carrier induced Moss-Burstein shift results in a large effective optical band gap. The model is supported by neutron diffraction, which reveals that the oxygen sublattice is only 98.4% occupied, thus confirming oxygen substoichiometry as the electron source.

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