%X 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.
%C US
%O © 2011 American Physical Society
%L discovery1395992
%J Physical Review Letters
%D 2011
%A DO Scanlon
%A AB Kehoe
%A GW Watson
%A MO Jones
%A WI David
%A DJ Payne
%A RG Egdell
%A PP Edwards
%A A Walsh
%V 107
%T Nature of the band gap and origin of the conductivity of PbO2 revealed by theory and experiment.
%N 24