Ab initio study the effects of Si and Mg dopants on point defects and Y diffusion in YAG

Abstract

The effects of Si and Mg dopants on point defects and Y diffusion in YAG are studied by the ab inito DFT calculations. Introduction of Si in YAG could largely decrease the formation energies of cation vacancies. It will improve the concentration of cation vacancies and enhance the lattice diffusion. Mg dopant has the effect of reducing O vacancy formation energies. In the codoping condition, the Si and Mg ions shows agglomeration in YAG. It indicates that using both MgO and SiO2 as the sintering aids would form MgO–SiO2 liquid phase, which could enhance the densification rate. The calculated electronic structures show that the Si or Mg dopant does not introduce defect state in the band gap of YAG. The Si shows a strong covalent property and Mg shows a strong ionic property in YAG. The charged states almost have no effect on local structure, electronic structure and effective charge of the dopants. We also studied the effect of Si and Mg dopants on Y diffusion via vacancy mechanism on the Y, Al(tet) and Al(oct) sublattices. The results show that Si and Mg dopants only slightly decrease the barrier energies of Y diffusion, indicating Si and Mg dopants enhance Y diffusion mainly through promoting the formation of cation vacancy or liquid phase.