Scanlon, DO; Kehoe, AB; Watson, GW; Jones, MO; David, WI; Payne, DJ; Egdell, RG; ... Walsh, A; + view all Scanlon, DO; Kehoe, AB; Watson, GW; Jones, MO; David, WI; Payne, DJ; Egdell, RG; Edwards, PP; Walsh, A; - view fewer (2011) Nature of the band gap and origin of the conductivity of PbO2 revealed by theory and experiment. Physical Review Letters , 107 (24) , Article 246402. 10.1103/PhysRevLett.107.246402.

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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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