AI Article Synopsis
- Lead dioxide (PbO2), used in lead-acid batteries, raises questions about its classification as a metal or semiconductor and its high conductivity.
- Research indicates that PbO2 behaves as an n-type semiconductor with a small indirect band gap of around 0.2 eV, primarily due to oxygen vacancies acting as electron carriers.
- Neutron diffraction studies support the finding that the oxygen sublattice is 98.4% occupied, confirming that the electron source is linked to oxygen substoichiometry.
Article Abstract
Lead dioxide has been used for over a century in the lead-acid battery. Many fundamental questions concerning PbO2 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 PbO2, using a hybrid density functional, and show that it is an n-type semiconductor with a small indirect band gap of ∼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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| http://dx.doi.org/10.1103/PhysRevLett.107.246402 | DOI Listing |
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