DFT study of carbon-related defects in yttrium aluminum garnet in a CO-containing atmosphere

Using density functional theory combined with thermochemical data, we analyze the formation of native and carbon-related defects in yttrium aluminum garnet (YAG) grown in a CO-containing atmosphere. The concentrations of various defect species in as-grown YAG are computed as functions of the partial pressures of CO, CO2, and O2. Under reducing conditions, carbon preferentially forms negatively charged CO defects, whereas positively charged CAl defects at the tetrahedral 24(d) positions dominate under oxidizing conditions. Only a small fraction of carbon-related defects (approximately 1%) participate in the formation of defect complexes. Carbon solubility in YAG is predicted to exhibit a pronounced minimum under moderately reducing conditions and to reach a maximum under either strongly reducing or oxidizing atmospheres. The formation of negatively charged CO defects in YAG grown under strongly reducing conditions significantly enhances the concentration of charged oxygen vacancies, leading to an increase of several orders of magnitude in their concentration.