Oxygen vacancy in perovskite oxides: Electron structure calculation by the SCF Xα, SW technique

Bunin, M. A.; Prosandeyev, S. A.; Gegusin, I. I.; Tennenboum, I. M.

doi:10.1080/10420159508227186

Cited by 5 publications

(6 citation statements)

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“…The simplest neutral oxygen vacancy is formed when a single O atom is removed from the cell (usually denoted as an F center), but even the electronic structure of such a simple defect has been subject to a large debate. Some studies suggest an essential role of the Ti 3d empty states in the electronic structure of the neutral F center (O vacancy with two electrons) [3][4][5], while others indicate a partial or total localization of the electrons in the vacancy [1,6]. There is also a qualitative contradiction in the literature regarding the position of the F center level in the optical band gap: whether it lies well below the conduction band bottom [3], close to it, or even falls inside the conduction band [5].…”

Section: Introductionmentioning

confidence: 99%

“…Some studies suggest an essential role of the Ti 3d empty states in the electronic structure of the neutral F center (O vacancy with two electrons) [3][4][5], while others indicate a partial or total localization of the electrons in the vacancy [1,6]. There is also a qualitative contradiction in the literature regarding the position of the F center level in the optical band gap: whether it lies well below the conduction band bottom [3], close to it, or even falls inside the conduction band [5]. Considerable experimental efforts have also been made to study and understand the properties of defective SrTiO 3 , including the phenomenon for ionic transport [10] and the structural properties [11].…”

Section: Introductionmentioning

confidence: 99%

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First principles simulations of F centers in cubic SrTiO ₃

Carrasco

Illas

López

et al. 2005

phys. stat. sol. (c)

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Atomic and electronic structure of regular and O-deficient SrTiO 3 have been studied. Several types of first principles atomistic simulations: Hartree-Fock method, Density Functional Theory, and hybrid HF-DFT functionals, have been applied to periodic models that consider supercells of different sizes (ranging between 40 and 240 atoms). We confirm the ionic character of the Sr-O bonds and the high covalency of the Ti-O 2 substructure. For the stoichiometric cubic crystal; the lattice constant and bulk modulus correctly reproduce the experimental data whereas the band gap is only properly obtained by the B3PW functional. The relaxed geometry around the F center shows a large expansion of the two nearest Ti ions. Moreover, the vacancy formation energy is extremely sensitive to the size and the shape of the supercell as well as the calculation method. The electronic density map indicates the redistribution of two electrons of the missing O atom between the vacancy and 3d atomic orbitals of the two nearest Ti ions, in contrast to the F centers in ionic oxides where the charge centroid does not change.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First principles simulations of F centers in cubic SrTiO ₃

Carrasco

Illas

López

et al. 2005

phys. stat. sol. (c)

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“…However this computation is in line with other computations of V O in perovskites showing the presence of deep V O states of the F -center type. 6,7,8,10,11 This puzzle should be resolved somehow.…”

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confidence: 99%

“…Theoretical studies 3,4 did not consider the states of the F -center-type (a vacancy centered, symmetric electron density), but, later, computations showed that the states of the F -center type , in the single charged oxygen vacancy (V + O ), can have lower energy than the states of the V ++ O Ti 3+ -type 6,7,8 . However, the EPR signal of such states has not been found experimentally.…”

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confidence: 99%

Comment on “Conduction states in oxide perovskites: Three manifestations ofTi3+Jahn-Teller polarons in barium titanate”

2004

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In this comment to S. Lenjer, O. F. Schirmer, H. Hesse, and Th. W. Kool, Phys. Rev. B 66, 165106 (2002), we discuss the electronic structure of oxygen vacancies in perovskites. First-principles computations are in favor of rather deep levels in these vacancies, and Lenjer et al. even suggest that the electrons' interaction energy is negative. However, data on electroconductivity are against both these scenarios.It has been well established by gravimetric measurements that the thermal annealing of BaTiO 3 results in reversible changes of the oxygen content. 1,2 Computations in the framework of the shell model 3,4 as well as the quasichemical reactions approach (based on the dependence of conductivity on oxygen partial pressure 5-7 ) showed that, after annealing at 1000 K Ͼ T Ͼ 500 K, the main defects are of Shottky type, and the appearance of oxygen vacancies ͑V O ͒ is much more probable than the vacancies on other sites. This has been confirmed, for instance, by experiments on electroconductivity (see Ref. 8 and references therein) and oxygen diffusion (with isotopes). 9 The increase of the V O concentration increases n-type conductivity. At a large V O concentration, their ordering by the formation of shear planes can take place. 10 Reduction of the samples changes the color from transparent light-yellow to blue, and, at large concentration, to black. There appears characteristic absorbtion of light. 11 Doping the samples with p-type impurities is compensated by the appearance of V O at annealing.Annealing in the oxygen atmosphere decreases n-type conductivity and p-type conductivity can appear at a large exposure time. This is usually interpreted as the presence in the samples (even single crystals) of unavoidable p-type impurities. Depending on the degree of the compensation of V O and p-type impurities, V O can accept two electrons (neutral vacancy), single charged V O + has one electron, and, finally, V O ++ without electrons is double charged. Also, V O + and V O can have a high degree of compensation (hdc) (the Fermi level coincides with the energy level position) or low degree of compensation (ldc) (the Fermi level is at the middle between the energy level and the conduction band bottom. Thus, the oxygen vacancy is a multiple-charge center and, in order to treat the thermodynamics of electrons on such centers one has to consider the grand canonical ensemble. 8 Electroconductivity data show that all these states can be observed if one varies the degree of the defects' compensation 8 (see Table I). Note that these energies were observed in samples having different values of conductivity: very high for V O and much smaller for V O + . These samples had different color: black or gray (very small activation energies inherent to V O ) or light-yellow (comparatively deep levels corresponding to V O + ). By using electron paramagnetic resonance (EPR) spectroscopy, Scharfschwerdt et al. 12 found a signal in reduced BaTiO 3 which they attributed to a symmetry broken state of Ti 3+ bound to V O ++ ͑V O ++ Ti 3+ ͒. S...

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“…In these phase transitions, the atomic displacements from their ideal positions in the cubic structure are relatively small [1][2][3][4][5][6]. It has been observed that these materials can contain oxygen vacancies [7]. Their content is strongly dependent on the preparation method and on the subsequent thermal treatments.…”

Section: Introductionmentioning

confidence: 99%

Perturbed angular correlation study of 181Ta-doped PbTi1−xHfxO3 compounds

Alonso

García

Rubia

et al. 2012

Physica B: Condensed Matter

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In this work, the hyperfine quadrupole interaction at Ta-doped PbTi} _ x Hf x 0 3 polycrystalline samples is studied for the first time. Powders with x=0.25, 0.50 and 0.75 were prepared and characterized by X-ray diffraction analysis. Perturbed Angular Correlation (PAC) analyses were done as a function of temperature, using low concentration lsl Ta nuclei as probes. In the ferroelectric and paraelectric phases of these compounds two sites were occupied by the probes. For each site the quadrupole frequency, asymmetry and relative distribution width parameters were obtained as a function of temperature above and below the Curie temperature (T c ). One of these sites was assigned to the regular Ti-Hf site, while the other one was assigned to some kind of defect. The behavior of the hyperfine parameters as a function of temperature was analyzed in terms of a recent published phase diagram and the presence of disorder below and above T c . For the three compositions measured, the obtained hyperfine parameters present discontinuities which correspond to the ferroelectric-paraelectric phase transition. In both phases it was found broad frequency distributed interactions. The disorder in the electronic distribution would be responsible for the broad line width of the hyperfine interaction.

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Oxygen vacancy in perovskite oxides: Electron structure calculation by the SCF Xα, SW technique

Cited by 5 publications

References 5 publications

First principles simulations of F centers in cubic SrTiO ₃

First principles simulations of F centers in cubic SrTiO ₃

Comment on “Conduction states in oxide perovskites: Three manifestations ofTi3+Jahn-Teller polarons in barium titanate”

Perturbed angular correlation study of 181Ta-doped PbTi1−xHfxO3 compounds

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Oxygen vacancy in perovskite oxides: Electron structure calculation by the SCF Xα, SW technique

Cited by 5 publications

References 5 publications

First principles simulations of F centers in cubic SrTiO 3

First principles simulations of F centers in cubic SrTiO 3

Comment on “Conduction states in oxide perovskites: Three manifestations ofTi3+Jahn-Teller polarons in barium titanate”

Perturbed angular correlation study of 181Ta-doped PbTi1−xHfxO3 compounds

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First principles simulations of F centers in cubic SrTiO ₃

First principles simulations of F centers in cubic SrTiO ₃