Investigation of Native Point Defects and Nonstoichiometry Mechanisms of Two Yttrium Silicates by First‐Principles Calculations

First‐principles method is used to study the native point defects in Y 2 SiO 5 and Y 2 Si 2 O 7 silicates. The calculated defect formulation energies show similar native point defect behaviors in Y 2 SiO 5 and Y 2 Si 2 O 7 : the oxygen Frenkel defect is predominant; and it is followed by the cation antisite and Schottky defects. The possible chemical potential range of each constituent is further considered in the calculation of defect formation energy. Oxygen interstitial (O i ) and oxygen vacancy ( V O ) are the predominant native point defects under O‐rich and O‐poor condition, respectively. In addition, the mechanisms of accommodating composition deviations from stoichiometric Y 2 SiO 5 and Y 2 Si 2 O 7 are investigated. For Y 2 SiO 5 , Y 2 Si 2 O 7 impurity may appear, together with the defects of Si Y antisite, O i interstitial, and/or V Y vacancy when SiO 2 is excess; while Y Si antisite appears together with Y i interstitial and/or V O vacancy in Y 2 SiO 5 when Y 2 O 3 is excess. For Y 2 Si 2 O 7 , the main process is the formation of Si Y antisite accompanied by O i interstitial and/or V Y vacancy when SiO 2 is excess; but Y 2 SiO 5 impurity forms, together with Y Si antisite, V O vacancy, and/or Y i interstitial in Y 2 Si 2 O 7 when Y 2 O 3 is excess. We expect that the results are useful to control of processing conditions and further to optimization of performance of the two silicate