Theoretical investigation of carbon defects and diffusion in alpha-quartz - art. no. 085333

The geometries, formation energies, and diffusion barriers of carbon point defects in silica (a-quartz) have been calculated using a charge-self-consi stent density-functional based nonorthogonal tight-binding method. It is fo und that bonded interstitial carbon configurations have significantly lower formation energies (on the order of 5 eV) than substitutionals. The activa tion energy of atomic C diffusion via trapping and detrapping in interstiti al positions is about 2.7 eV. Extraction of a CO molecule requires an activ ation energy <3.1 eV but the CO molecule can diffuse with an activation ene rgy <0.4 eV. Retrapping in oxygen vacancies is hindered-unlike for O-2-by a barrier of about 2 eV.