Mechanisms of Mono-Vacancy and Oxygen Permeability in Y_2SiO_5 Orthosilicate Studied by First-Principles Calculations

摘要

Understanding the mechanisms of native point defects and oxygen-vacancy diffusion in Y_2SiO_5 is important to evaluate its performance as environmental and thermal barrier coating (ETBC). In the present first-principles calculations, we show that oxygen vacancy is the predominant vacancy species and prefers to form on the oxygen lattice sites inside SiO_4 tetrahe-dra instead of on the interstitial non-silicon-bonded oxygen site. The calculated defect formation energy and concentration of mono-vacancies in Y_2SiO_5 obviously depend on the chemical potential of each element. The results suggest that it is possible to tailor the vacancy species in Y_2SiO_5 by controlling the chemical environment in material synthesis. Finally, theoretical simulation revealed that the self-diffusion of oxygen vacancy has high energy barriers in Y_2SiO_5, which is comparable to those in SiO_2 and Al_2O_3. The result demonstrates low oxygen permeability in Y_2SiO_5 and further strengthens its promising applications as ETBC material.