Atomistic Modeling of Native Point Defects in Yttrium Aluminum Garnet Crystals

Native point defects in yttrium aluminum garnet (YAG) are studied in the framework of the pair-potential approximation, coupled with the shell-model description of the lattice ions. For the perfect lattice, a new set of potential parameters is obtained; these parameters reproduce the structure, elastic, and dielectric constants of YAG very well. The calculated formulation energies for native defects suggest that antisite disorder is preferred over Frenkel and Schottky-like disorder in YAG. The calculated values of the distortion that is caused by the antisite Y atom that substitutes in the Al site in the lattice are in excellent agreement with the extended X-ray absorption fine-structure (EXAFS) measurements. In nonstoichiometric YAG, the calculated reaction energies indicate that excess Y2O3 or Al2O3 most likely is accommodated by the formation of antisites, rather than vacancies, in the lattice.