Ab initiostudy of structural and electronic properties of yttria-stabilized cubic zirconia

Ab initio calculations have been performed on the structural and electronic properties of pure zirconia and yttria-stabilized cubic zirconia (YSZ). We use the local-density approximation to the exchange and correlation energy functional. We expand the Kohn-Sham orbitals in plane waves and use norm-conserving fully separable pseudopotentials. We find, in agreement with experiments that the most stable phase at zero temperature and pressure is the monoclinic baddelyte structure which transforms under pressure in the brookite orthorhombic phase. We then study the properties of the YSZ cubic phase using a supercell of 96 atoms. This is a defective structure where oxygen vacancies and yttrium substitutional impurities play a major role. The pattern of relaxation around the defects is consistent with the most recent scattering data, as well as their relative interaction which leads to a next-nearest-neighbor attraction between vacancy and yttrium. The analysis of the electronic properties show that single occupied color centers ${\mathrm{F}}^{+}$ are only marginally stable and decay into neutral, doubly occupied F centers and empty (doubly charged) vacancies. Therefore, we found that the ${\mathrm{F}}^{+}$ center in YSZ is a negative Hubbard-$U$ site.