Abstract
We computed the atomic shift sizes of the closest adjacent atoms adjoining the (001) surface F-center at ABO3 perovskites. They are significantly larger than the atomic shift sizes of the closest adjacent atoms adjoining the bulk F-center. In the ABO3 perovskite matrixes, the electron charge is significantly stronger confined in the interior of the bulk oxygen vacancy than in the interior of the (001) surface oxygen vacancy. The formation energy of the oxygen vacancy on the (001) surface is smaller than in the bulk. This microscopic energy distinction stimulates the oxygen vacancy segregation from the perovskite bulk to their (001) surfaces. The (001) surface F-center created defect level is nearer to the (001) surface conduction band (CB) bottom as the bulk F-center created defect level. On the contrary, the SrF2, BaF2 and CaF2 bulk and surface F-center charge is almost perfectly confined to the interior of the fluorine vacancy. The shift sizes of atoms adjoining the bulk and surface F-centers in SrF2, CaF2 and BaF2 matrixes are microscopic as compared to the case of ABO3 perovskites.
Highlights
In the last 50 years, great attention has been paid to an in-depth understanding of the radiation formation of lattice defects in alkali and alkaline earth metal halides, as well as in simple and complex oxides
In order to obtain as good as possible results for the band gaps of SrF2, BaF2 and CaF2 fluorites, as well as SrZrO3, PbTiO3, BaTiO3 and SrTiO3 perovskites, we performed our ab initio computations by means of the B3PW hybrid exchange-correlation functional
The B3PW functional, since it is a superposition of HF and density functional theory (DFT) methods, is much better suited for our band gap and optical property ab initio computations in SrF2, BaF2, CaF2, SrZrO3, PbTiO3, BaTiO3 and SrTiO3 matrixes
Summary
In the last 50 years, great attention has been paid to an in-depth understanding of the radiation formation of lattice defects in alkali and alkaline earth metal halides, as well as in simple and complex oxides. In order to obtain as good as possible results for the band gaps of SrF2 , BaF2 and CaF2 fluorites, as well as SrZrO3 , PbTiO3 , BaTiO3 and SrTiO3 perovskites, we performed our ab initio computations by means of the B3PW hybrid exchange-correlation functional. The B3PW functional, since it is a superposition of HF and DFT methods, is much better suited for our band gap and optical property (defect level positions in the band gap) ab initio computations in SrF2 , BaF2 , CaF2 , SrZrO3 , PbTiO3 , BaTiO3 and SrTiO3 matrixes. Our B3PW computed oxygen vacancy formation energies are equal to 7.55, 7.82, 10.30 and 7.10 eV in SrZrO3 , PbTiO3 , BaTiO3 and SrTiO3 perovskites (Table 3 and Figure 4). Our computed band-gap widths for the SrF2 , BaF2 and CaF2 containing the single bulk fluorine vacancy at the Γ point are equal to 11.34, 11.28 and 10.99 eV, respectively (Table 4). B3PW computations, the strong increase of the chemical bond covalency between the adjacent Ti atoms and the BaTiO3 bulk F-center equivalent to 0.320 e
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