<i>Ab initio</i> calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies

Rusevich, Leonid L.; Kotomin, E. A.; Zvejnieks, G.; Попов, А. И.

doi:10.1063/10.0002472

Cited by 29 publications

(30 citation statements)

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“…3 c). It is worth mentioning that in perovskites with lower (than cubic) crystal symmetry, the magnitudes of the B -Vo- B elongations and, hence, of the dipole components can differ for vacancies in different atomic planes 9 , 15 . However, this difference does not affect the dipolar orientation, which here is of central importance.…”

Section: Resultsmentioning

confidence: 99%

“…3 e). Interestingly, the energies for vacancy formation in different atomic planes may differ in magnitude by ~ 10% 8 , 10 , 15 , but the energies E DC and E DA can differ dramatically because of their signs 14 . Thus, the elastic properties, rather than the formation energy, can determine a type of the atomic planes, where vacancies are located in epitaxial films.…”

Section: Resultsmentioning

confidence: 99%

“…The nearest to vacancy Ti-cations shift away from the vacancy along the Ti–O-Ti–O-direction. The Ti-Vo-Ti distance elongates compared to the Ti–O-Ti distance 14 , 15 . This elongation is the primary mechanism, which determines the emergence of stress around the vacancy.…”

Section: Introductionmentioning

confidence: 97%

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Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Tyunina

Pacherová

Kocourek

et al. 2021

Sci Rep

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In scientifically intriguing and technologically important multifunctional ABO3 perovskite oxides, oxygen vacancies are most common defects. They cause lattice expansion and can alter the key functional properties. Here, it is demonstrated that contrary to weak isotropic expansion in bulk samples, oxygen vacancies produce strong anisotropic strain in epitaxial thin films. This anisotropic chemical strain is explained by preferential orientation of elastic dipoles of the vacancies. Elastic interaction of the dipoles with substrate-imposed misfit strain is suggested to define the dipolar orientation. Such elastic behavior of oxygen vacancies is anticipated to be general for perovskite films and have critical impacts on the film synthesis and response functions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Tyunina

Pacherová

Kocourek

et al. 2021

Sci Rep

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“…The two unpaired electron spins arise after the removal of an oxygen atom. The spins are distributed among Ti atoms, which are not necessarily the nearest ones to the vacancy, as we noted before for BaTiO 3 31 . An additional occupied local energy level or a band emerge in the band gap due to the formation of defects.…”

Section: Resultsmentioning

confidence: 68%

“…When an oxygen atom is removed from STO and a neutral vacancy V O is formed, the spins of the two unpaired electrons are distributed among the Ti atoms near the vacancy. This system may have two different spin states: either S z = 0 (the singlet state; two antiparallel spins) or S z = 1 (the triplet state; two spins are parallel) 31 , 32 . Concurrently, the removal of an O 2− anion produces a charged oxygen vacancy V O 2+ , around which all chemical bonds are closed 32 .…”

Section: Methodsmentioning

confidence: 99%

The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions

Rusevich

Tyunina

Kotomin

et al. 2021

Sci Rep

Self Cite

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The electronic properties, including bandgap and conductivity, are critical for nearly all applications of multifunctional perovskite oxide ferroelectrics. Here we analysed possibility to induce semiconductor behaviour in these materials, which are basically insulators, by replacement of several percent of oxygen atoms with nitrogen, hydrogen, or vacancies. We explored this approach for one of the best studied members of the large family of ABO3 perovskite ferroelectrics — strontium titanate (SrTiO3). The atomic and electronic structure of defects were theoretically investigated using the large-scale first-principles calculations for both bulk crystal and thin films. The results of calculations were experimentally verified by studies of the optical properties at photon energies from 25 meV to 8.8 eV for in-situ prepared thin films. It was demonstrated that substitutions and vacancies prefer locations at surfaces or phase boundaries over those inside crystallites. At the same time, local states in the bandgap can be produced by vacancies located both inside the crystals and at the surface, but by nitrogen substitution only inside crystals. Wide-bandgap insulator phases were evidenced for all defects. Compared to pure SrTiO3 films, bandgap widening due to defects was theoretically predicted and experimentally detected.

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Oxygen Defect Formation Thermodynamics of CaMnO₃: A Closer Look

Grimm

Bredow

2022

Physica Status Solidi (b)

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Hydrogen is one of the most promising future energy sources. [1] In contrast to conventional energy sources, only water is produced during its combustion. At present, a large amount of hydrogen is still obtained from hydrocarbons by steam reforming. [2] However, for every two molecules of hydrogen, one molecule of carbon dioxide is also produced, therefore this process is not climate neutral. Therefore, the sustainable production of hydrogen is of primary interest for the future of the energy industry. [3] One possibility is electrolytic water splitting. [4] The problem, however, is the high demand for environmentally friendly-generated electricity, which is not yet sufficiently available. A promising alternative is solar or solar-thermal water splitting by electrolysis, thermochemistry or photocatalysis. This is not yet feasible on a large scale due to technical and economic challenges. Photocatalysis, on the other hand, does not depend on an external supply of electricity or heat, but requires special catalysts that are often too expensive or resource critical.In this respect, the combination of chemical and electrical potentials is advantageous. If an anode material is used which is itself redox active, the potential required for electrolysis can be reduced. Perovskites ABO 3 are suitable materials due to their stability and temperature-dependent reversible loss of oxygen and high oxygen mobility in the lattice. [5,6] One of the perovskites which have recently attracted interest is CaMnO 3 . Poeppelmeier et al. discuss the low-temperature synthesis of oxygen-deficient CaMnO 2.5 starting from polycrystalline CaMnO 3 . [7] X-ray and neutron diffraction patterns were used to determine the crystal structure and distribution of oxygen vacancies in CaMnO 2.5 . Jung et al. determined the electronic band structures of CaMnO 3 and LaMnO 3 measuring reflectivity spectra at room temperature. [8] Wollan and Koehler studied the magnetic properties of perovskite-type compounds ½La ð1ÀxÞ , Ca x MnO 3 uses neutron diffraction. [9] Several antiferromagnetic (AFM) spin states were found for x ¼ 0 and x ≥ 0.5. Between x ¼ 0 and x ¼ 0.5, they observed simultaneous occurrence of ferromagnetic and AFM structures. In a narrow range around x ¼ 0.35 the structure was found to be ferromagnetic. The measured magnetic moments decrease with higher x values. Bakken et al. measured the variation of oxygen nonstoichiometry of CaMnO 3-δ with the oxygen partial pressure at 1223, 1273, and 1323 K. [10] The dependence of partial molar enthalpy and entropy from δ was derived. Bulfin et al. measured the equilibrium nonstoichiometry of CaMnO 3 and Ca 0.8 Sr 0.2 MnO 3 for temperatures in the range 400-1200 °C and different oxygen partial pressures. [11] Ca 0.8 Sr 0.2 MnO 3 showed a lower enthalpy of reduction and was also robust against phase transition, different from CaMnO 3 at high temperatures. Also a number of computational studies on CaMnO 3 using density functional theory (DFT) have been published. Molinari et al. calculated the structural, e...

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Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies

Cited by 29 publications

References 60 publications

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions

Oxygen Defect Formation Thermodynamics of CaMnO₃: A Closer Look

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Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies

Cited by 29 publications

References 60 publications

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions

Oxygen Defect Formation Thermodynamics of CaMnO3: A Closer Look

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Oxygen Defect Formation Thermodynamics of CaMnO₃: A Closer Look