First principles hybrid Hartree-Fock-DFT calculations of bulk and (001) surface F centers in oxide perovskites and alkaline-earth fluorides

Abstract

We report the results of ab initio calculations and analysis of systematic trends for the F centers in the bulk and on the (001) surface in oxide perovskites, such as BaTiO 3 , SrTiO 3 , SrZrO 3 , and PbZrO 3 , with a corresponding comparison of the F centers in perovskites with those in alkaline earth metal fluorides (CaF 2 , BaF 2 , and SrF 2 ). It was found that in perovskites in both bulk F centers and those on their (001) surfaces, two nearest to the vacancy Ti or Zr atoms repel each other, while the next nearest O atoms relax towards the oxygen vacancy. It was also found that the obtained relaxations of atoms in the nearest neighborhood around the F center in ABO 3 perovskites are generally larger than in alkaline earth metal fluorides. The bulk and (001)-terminated surface F center ground states in BaTiO 3 , SrTiO 3 , and SrZrO 3 perovskites are located 0.23, 0.69, 1.12 eV, and 0.07, 0.25, 0.93 eV, respectively, below the conduction band bottom, indicating that the F center is a shallow donor. The vacancies in BaTiO 3 , SrZrO 3 , and PbZrO 3 are occupied with 1.103e, 1.25e, and 0.68e, respectively, whereas slightly smaller charges, only 1.052e, 1.10e, and 0.3e are localized inside the F center on the perovskite (001) surface. In contrast to the partly covalent ABO 3 perovskites, charge is well localized (around 80 %) inside the ionic CaF 2 , BaF 2 , and SrF 2 fluorine vacancy.

Molecular crystals vs. superatomic lattice: a case study with superalkali-superhalogen compounds

“…However, we acknowledge that the accuracy of bandgap calculations can be enhanced by using hybrid or self-interaction-corrected functionals. 40,41…”

“…However, we acknowledge that the accuracy of bandgap calculations can be enhanced by using hybrid or self-interaction-corrected functionals. 40,41 Fig. 9 and 10 represent the electronic band structure and density of states (DOS), respectively, for dZnS of the N 4 Mg 6 M-AlX 4 supersalts.…”

Role of Sr doping and external strain on relieving bottleneck of oxygen diffusion in La2−xSrxCuO4−δ

“…2a, E V of O decrease linearly with tensile strain at a similar rate regardless of their charge states. In most ionic crystals and perovskite materials such as BaTiO 3 , SrTiO 3 , SrZrO 3 , and PbZrO 3 , cations around anionic vacancy move away from each other 49 , indicating the strong Coulomb repulsions between the cations. This induces strong local compressive stress in the crystal and if the crystal is allowed to relax, the equilibrium lattice constants along the a-and b-axes increase by 0.6% for n = 0 case of our supercell geometry.…”

Tendencies in ABO3 Perovskite and SrF2, BaF2 and CaF2 Bulk and Surface F-Center Ab Initio Computations at High Symmetry Cubic Structure

“…The V 0 is the most frequent point defect in ABO 3 perovskites [23][24][25][26][27]. Bearing in mind the technological relevance of ABO 3 perovskite matrixes, as well as quantity of F-centers, which unavoidably exist in these materials and deteriorate their quality, the number of F-center studies is still insufficient [28][29][30][31][32][33][34][35]. In order to save the computer time, we performed bulk and (001) surface F-center ab initio computations in ABO 3 perovskites in their high-symmetry cubic phase.…”