Atomistic and electronic structure of antisite defects in yttrium aluminum garnet: Density-functional study

First-principles density-functional theory calculations have been performed on the atomistic structure, electronic structure, and distribution of antisite defects (AD) in yttrium aluminum garnet (YAG) Y3 Al5 O12. The formations of one and two antisite defects per unit cell are endothermic and the formation energy per defect is lower in 2AD than in 1AD. In the most stable 1AD structure, Y and Al are as close as possible and two oxygen atoms become unbound to Al rising the energy of their (highest) valence levels and introducing a defect level in the gap 0.25 eV above the top of the perfect YAG valence band. The binding energy between the individual substitutional defects YAl and AlY to form 1AD is 0.74 eV. The most stable 2AD structure is made of two single ADs linked together with one AlO6 moiety and it has basically the same electronic structure as the most stable 1AD; it is the only 2AD structure that preserves the inversion center with respect to the unit-cell center. In this case, the binding energy between two single ADs is 0.22 eV.