Electron Spin Resonance in Semiconducting Rutile

Chester, P. F.

doi:10.1063/1.1777049

Cited by 143 publications

(46 citation statements)

References 8 publications

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“…It has been suggested that this position is the most stable for location of the titanium interstitial. 19,41 This is a reasonable assumption, since the environment for the titanium interstitial in this site is closer to that of Ti in bulk rutile. Different starting positions along the z axis were tested, and it was confirmed that the octahedral sites are the most stable positions for the titanium interstitials.…”

Section: A Point Defectsmentioning

confidence: 99%

Thermodynamics of oxygen defective Magnéli phases in rutile: A first-principles study

2008

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Ab initio thermodynamics has been used to calculate the formation energies, in different environmental conditions, for a number of oxygen-defective structures in rutile. In addition to the Ti n O 2n−1 ͑3 ഛ n ഛ 5͒ Magnéli phases, the two fundamental points defects, Ti interstitials and neutral oxygen vacancies, were also considered. The predicted phase stability is compared to available experimental data and there is reasonable agreement between the calculated phase boundaries and those observed. These results are used to discuss a mechanism that has been proposed as an explanation for the formation of the crystallographic shear planes in rutile.

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Section: A Point Defectsmentioning

confidence: 99%

Thermodynamics of oxygen defective Magnéli phases in rutile: A first-principles study

2008

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“…Experimental confirmation came from µSR detection of the muonium counterpart of such a state (Cox et al 2001a, Shimomura et al 2002, as well as ESR and ENDOR detection for hydrogen itself (Hofmann et al 2002) 12 . So far, only in ZnO has a shallow-donor hydrogen state been identified by conventional magnetic resonance, although previously unexplained features associated with hydrogen in the ESR spectra of rutile-TiO 2 deserve further investigation in this light (Chester 1961(Chester , 2004. Considering the possibility that hydrogen might act similarly as an adventitious dopant in other oxides, the present paper (II) is devoted mainly to binary oxides that are visually transparent, i.e.…”

Section: Context and Scope Of The Articlementioning

confidence: 99%

Oxide muonics: II. Modelling the electrical activity of hydrogen in wide-gap and high-permittivity dielectrics

Cox

Gavartin

Lord

et al. 2006

J. Phys.: Condens. Matter

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Following the prediction and confirmation that interstitial hydrogen forms shallow donors in zinc oxide, inducing electronic conductivity, the question arises as to whether it could do so in other oxides, not least in those under consideration as thin-film insulators or high-permittivity gate dielectrics. We have screened a wide selection of binary oxides for this behaviour, therefore, using muonium as an accessible experimental model for hydrogen. New examples of the shallow-donor states that are required for n-type doping are inferred from hyperfine broadening or splitting of the muon spin rotation spectra. Electron effective masses are estimated (for several materials where they are not previously reported) although polaronic rather than hydrogenic models appear in some cases to be appropriate. Deep states are characterized by hyperfine decoupling methods, with new examples found of the neutral interstitial atom even in materials where hydrogen is predicted to have negative-U character, as well as a highly anisotropic deep-donor state assigned to a muonium-vacancy complex. Comprehensive data on the thermal stability of the various neutral states are given, with effective ionization temperatures ranging from 10 K for the shallow to over 1000 K for the deep states, and corresponding activation energies between tens of meV and several eV. A striking feature of the systematics, rationalized in a new model, is the preponderance of shallow states in materials with band-gaps less below 5 eV, atomic states above 7 eV, and their coexistence in the intervening threshold range, 5-7 eV.

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“…The lineshape (see Fig. 4 for details) and the g-factor are typical features in the socalled A spectrum due to Ti 3+ ions 26,27 . Now we come to the question: how the Ti 3+ ions are generated after irradiation?…”

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Origin of magnetic moments in defectiveTiO2single crystals

et al. 2009

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In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, i.e. Ti 3+ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO6−x) stretching Raman mode. We elucidate that Ti 3+ ions with one unpaired 3d electron provide the local magnetic moments.Recently, ferromagnetism has been observed in nonmagnetically doped, but defective oxides, including TiO 2 1,2,3,4 . This kind of observation challenges the conventional understanding of ferromagnetism, which is rather due to spin-split states or bands. Thus, one fundamental question must be answered: where are the moments located? Intensive theoretical work has been performed to understand the ferromagnetism in defective oxides 5,6,7 . In these papers, the triplet states of p-like electrons, located at cation or oxygen vacancies, yield the local moments, leading to a kind of ferromagnetism without the involvement of 3d electrons. Experimentally the ferromagnetism in undoped TiO 2 has been found to relate with oxygen vacancies (O V ) 2,3 , however, its mechanism remains unclear. It is worth to note that Ti 3+ ions with one 3d electron are usually generated in slightly reduced TiO 2 . When O is removed, the excess electrons are unpaired 8 . They can occupy the nearby localized Ti 3d orbit and therefore convert Ti 4+ ions to Ti 3+ ions. In a reduced rutile TiO 2 (110) surface, such a defect complex, Ti 3+ -O V , has been well studied by first-principles calculations 9,10 and experimentally by resonant photoelectron diffraction 11 . Therefore, experimental work is needed to clarify whether the magnetic moments in defective TiO 2 is due to unpaired 3d electrons localized on Ti 3+ ions.Ion irradiation is a non-equilibrium and reproducible method of inducing defects. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies and interstitials. The amount of defects can be controlled by the ion fluence and energy. In this paper, we irradiated rutile TiO 2 single crystals with 2-MeV O ions, resulting in a projected range of 1.52 µm and a longitudinal straggling of 0.16 µm as calculated by SRIM code (The Stopping and Range of Ions in Matter) 12 . As a result of this irradiation, the formation of Ti/O vacancies/interstitials is expected 12 . We selected high-energy oxygen ions as projectiles to avoid the introduction of foreign elements. Moreover, from a ballistic point of view, the creation of oxygen vacancies is more efficient, e.g., by a factor of 1.5 larger than the Ti-vacancy creation. From SRIM calculations it is also evident that, at the given energy, the maximum atomic concentration of the implanted oxygen ions is by a factor of 500 smaller than the concentration of oxygen recoils. For the region of maximum defect creation, i.e., at the end of the ion range, those project...

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Electron Spin Resonance in Semiconducting Rutile

Cited by 143 publications

References 8 publications

Thermodynamics of oxygen defective Magnéli phases in rutile: A first-principles study

Thermodynamics of oxygen defective Magnéli phases in rutile: A first-principles study

Oxide muonics: II. Modelling the electrical activity of hydrogen in wide-gap and high-permittivity dielectrics

Origin of magnetic moments in defectiveTiO2single crystals

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