Structures and energetics of point defects with charge states in zircon: A first-principles study.

The fundamental problem of point defects under different phase equilibrium conditions in zircon (ZrSiO 4 ) is carried out by first-principles calculation. The formation energies with the structural deformation of various native defects, i.e., single vacancy, interstitial, Frenkel and Schottky pairs at different charge states are calculated, which agree well with the available results. We identify V O 2 + shows an important role in non-stoichiometric regime of ZrSiO 4− x ( x  < 1). When Fermi level ( ε F ) locates close to the CBM, the V Zr 4 − becomes more easily observed than V O 2 + in O-rich environment. In turn, the most abundant interstitial defects are I Zr 4 + and I Si 4 + . The non-interacting Si Frenkel-pair, made of the association of quadruply charged defect in energy of 5.947 eV, is more likely to form than other type of Frenkel-pairs. By formation the complex defects associating partial and full Schottky defects requires higher formation energy. These results provide a good reference to understand storage state as well as disposal of excess weapons-grade Pu and high-actinide wastes. [ABSTRACT FROM AUTHOR]