Photoinduced electron paramagnetic resonance study of electron traps in TiO2 crystals: Oxygen vacancies and Ti3+ ions

Yang, Shan; Halliburton, L. E.; Manivannan, A.; Bunton, Patrick; Baker, David B.; Klemm, Matthias; Horn, S.; Fujishima, Akira

doi:10.1063/1.3124656

Cited by 99 publications

(79 citation statements)

References 18 publications

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“…The computed magnetic ground state is compatible with the evidence of triplet and doublet signals obtained in EPR measurements 59,60 …”

Section: Rutilesupporting

confidence: 65%

“…Electron paramagnetic resonance (EPR) measurements also confirmed the presence of Ti 3+ ionic species formed as a consequence of electron trapping at Ti 4+ centers in TiO 2−x crystals. 59,60 Notice that the localization of the unpaired electrons at Ti 3+ centers is correctly described only within the hybridfunctional scheme, 61 at variance with the case of standard local/semilocal functionals which commonly fail, due to incomplete cancellation of the self-interaction error. Notice also that the above physical picture is correctly captured only at the level of spin-polarized DFT, while neglecting spin polarization leads to a completely different description, with the excess charge trapped in the vacancy void, 49,53 in a configuration typical of a color center (F center).…”

Section: Rutilementioning

confidence: 99%

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Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: The case of oxygen vacancies in metal oxides

Gerosa

Bottani

Caramella

et al. 2015

The Journal of Chemical Physics

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We investigate the behavior of oxygen vacancies in three different metal-oxide semiconductors\ud (rutile and anatase TiO2, monoclinic WO3, and tetragonal ZrO2) using a recently proposed hybrid\ud density-functional method in which the fraction of exact exchange is material-dependent but obtained\ud ab initio in a self-consistent scheme. In particular, we calculate charge-transition levels relative to the\ud oxygen-vacancy defect and compare computed optical and thermal excitation/emission energies with\ud the available experimental results, shedding light on the underlying excitation mechanisms and related\ud materials properties. We find that this novel approach is able to reproduce not only ground-state\ud properties and band structures of perfect bulk oxide materials but also provides results consistent\ud with the optical and electrical behavior observed in the corresponding substoichiometric defective\ud systems. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.493180

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“…The computed magnetic ground state is compatible with the evidence of triplet and doublet signals obtained in EPR measurements 59,60 …”

Section: Rutilesupporting

confidence: 65%

Section: Rutilementioning

confidence: 99%

Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: The case of oxygen vacancies in metal oxides

Gerosa

Bottani

Caramella

et al. 2015

The Journal of Chemical Physics

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“…10,29-31 Similar gap state features attributed to occupied Ti states have been observed experimentally in a number of reduced TiO 2 samples exhibiting both intrinsic and extrinsic n-type defects. 32,33 In the case of O-deficient TiO 2 , electron paramagnetic resonance data show that the excess electrons are strongly localized at titanium sites near the vacancy, 34,35 with similar localization reported for fluorine-doped rutile TiO 2 , 36 and this polaronic localization of excess charge in n-type TiO 2 is supported by a number of theoretical studies. [37][38][39][40][41][42][43][44][45][46][47] Previous theoretical studies of Li-intercalated TiO 2 have supported the transfer of charge to Ti sites.…”

Section: Introductionmentioning

confidence: 60%

GGA+Udescription of lithium intercalation into anataseTiO2

2010

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We have used density-functional theory ͓generalized gradient approximation ͑GGA͔͒ to study lithium intercalation at low concentration into anatase TiO 2 . To describe the defect states produced by Li doping a Hubbard "+U" correction is applied to the Ti d states ͑GGA+ U͒. Uncorrected GGA calculations predict Li x TiO 2 to be metallic with the excess charge distributed over all Ti sites, whereas GGA+ U predicts a defect state 0.96 eV below the conduction band, in agreement with experimental photoelectron spectra. This occupied defect state corresponds to charge strongly localized at a single Ti 3d site neighboring the intercalated lithium with a magnetization of 1 B. This polaronic state produces a redshifted optical absorption spectrum, which is compared to those for the native O-vacancy and Ti-interstitial defects. The strong localization of charge at a single Ti center lowers the symmetry of the interstitial geometry relative to that predicted by GGA. The intercalated lithium sits close to the center of the octahedral site, occupying a single potential energy minimum with respect to displacement along the ͓001͔ direction. This challenges the previous interpretation of neutron diffraction data that there exist two potential energy minima separated by 1.6 Å along the ͓001͔ direction within each octahedron. Nudged elastic band calculations give barriers to interoctahedral diffusion of ϳ0.6 eV, in good agreement with experimental data. These barrier heights are found to depend only weakly on the position of the donated electron. The intercalation energy is 2.14 eV with GGA and 1.88 eV with GGA+ U, compared to the experimental value of ϳ1.9 eV. Li-electron binding energies have also been calculated. The ͓Li i• -Ti Ti Ј ͔ complex has a binding energy of 56 meV, and a second electron is predicted to be bound to give ͓Li i• -2Ti Ti Ј ͔ with a stabilization energy of 30 meV, indicating that intercalated lithium will weakly trap excess electrons produced during photoillumination or introduced by additional n-type doping.

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“…Despite the existence of many studies about defects in rutile TiO 2 , both experimental [20][21][22][23][24][25][26][27][28] and theoretical [21,25], there are few works on the intrinsically defective Magnéli phases [29][30][31][32][33][34][35]. Electronic structure calculations have been used to understand mainly the Ti 2 O 3 [32] and Ti 4 O 7 [29][30][31].…”

Section: Introductionmentioning

confidence: 99%

TinO2n−1Magnéli phases studied using density functional theory

et al. 2014

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Defects in the rutile TiO 2 structures have been extensively studied, but the intrinsic defects of the oxygendeficient Ti n O 2n−1 phases have not been given the same amount of consideration. Those structures, known as Magnéli phases, are characterized by the presence of ordered planes of oxygen vacancies, also known as shear planes, and it has been shown that they form conducting channels inside TiO-based memristor devices. Memristors are excellent candidates for a new generation of memory devices in the electronics industry. In this paper we present density-functional-theory-based electronic structure calculations for Ti n O 2n−1 Magnéli structures using PBESol+U (0 U 5 eV) and Heyd-Scuseria-Ernzerhof functionals, showing that intrinsic defects present in these structures are responsible for the appearance of states inside the band gap, which can act as intrinsic dopants for the enhanced conductivity of TiO 2 memristive devices.

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Photoinduced electron paramagnetic resonance study of electron traps in TiO2 crystals: Oxygen vacancies and Ti3+ ions

Abstract: Articles you may be interested inInsertion of lithium ions into TiO2 (rutile) crystals: An electron paramagnetic resonance study of the Liassociated Ti3+ small polaron

Cited by 99 publications

References 18 publications

Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: The case of oxygen vacancies in metal oxides

Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: The case of oxygen vacancies in metal oxides

GGA+Udescription of lithium intercalation into anataseTiO2

TinO2n−1Magnéli phases studied using density functional theory

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