A theoretical study was made of the effect of self-doping and of the contribution of native defects to the ionic conductivity of α-quartz. A thorough first-principles study was made of native defects in quartz, comprising Si and O defects in several charge states. On the basis of this comprehensive study of defect energetics, it was possible to evaluate the equilibrium concentrations of defects at a given temperature; including the effect of doping of the material, coming from its native defects. Under open conditions, the O partial pressure had an effect upon the concentrations and self-doping of the material. The results showed that the O interstitial was the native defect of highest concentration at equilibrium, and that charge compensation occurred between negative O interstitials and holes in the valence band. It was found that, in pure quartz, neutral defects were predominant at low temperatures and relatively high partial O pressures. However, at sufficiently low O pressures and sufficiently high temperatures, negative interstitials were expected to play a significant role in diffusion. The concentrations of the latter were low enough for their contribution to ionic conductivity to be negligible, but their sensitivity to the Fermi level was high. Therefore, if the Fermi level was increased, the intrinsic contribution to ionic conductivity would become important.

Density Functional Theory Investigation of Native Defects in SiO2 - Self-Doping and Contribution to Ionic Conductivity. G.Roma, Y.Limoge: Physical Review B, 2004, 70[17], 174101 (6pp)