Electrical Properties and Defect Chemistry of TiO 2 Single Crystal. I. Electrical Conductivity

Yadav

Journal of Experimental Nanoscience

et al. 2013

Fe-doped nanocrystalline samples of titanium oxide have been synthesised by sol-gel route and conventional sintering process at 450 C under atmospheric conditions. These samples are characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and dielectric property measurement. Samples with Fe content more than 4 mole% crystallises in rutile phase and those with less than 4 mole% crystallises in anatase phase. Nanocrystallite size has been controlled by Fe doping. Crystallite size was found to decrease with Fe concentration in the anatase phase samples whereas reverse happens in rutile phase samples of titanium oxide. There is a slight variation in numerical values of crystallite sizes measured by the two techniques: TEM and XRD peak broadening. The highest crystallite size was 86 nm in 10 mole% Fe-doped samples and the lowest 20 nm in 4 mole% Fe-doped sample. Large dispersions and anomalous values of the dielectric constant, "r were observed at low frequency in anatase phase samples. Rutile phase samples exhibit little dispersion over the measurement frequency range of 20 Hz to 10 MHz. The dielectric constant value of all the samples stabilises to a constant value at higher frequencies. This value is dependent on the final crystalline phase but independent of the crystallite size. The anomalous dielectric behaviour of anatase samples at low frequencies is assigned to the adsorbed -OH ions on the sample surface.

Section: Dielectric Studiessupporting

confidence: 54%

“…Parker and Wasilik [25] have studied the dielectric constant of single-crystal samples and suggested the separation of charge carriers at the opposite electrodes. Creation of charge carrier in TiO 2 due to oxygen vacancies in the doped TiO 2 samples has been reported by the several researchers [27][28][29][30].…”

Section: Dielectric Studiesmentioning

confidence: 99%

Dielectric properties of Fe-doped TiO₂nanoparticles synthesised by sol–gel route

Yadav

Journal of Experimental Nanoscience

et al. 2013

“…Among others, these studies include thermogravimetry 44,45 and electrical conductivity measurements. 14,45,46 Although the types of major defects in rutile are still under discussion, the studies generally conclude that TiO 2−x is oxygen deficient and that the predominant atomic point defects are interstitial titanium ions and/or oxygen vacancies.…”

Section: A Point Defectsmentioning

confidence: 99%

“…[9][10][11][12] Although very rare, titanium vacancies 13 have also been studied. Several experimental [13][14][15][16][17] and theoretical [4][5][6]12 investigations have been performed in order to understand the role that point defects play in determining the physical and chemical properties of TiO 2−x . Results of particular relevance to the current study will be discussed in Secs.…”

Section: Introductionmentioning

confidence: 99%

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

Liborio

Harrison

2008

Phys. Rev. B

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.

Journal of Applied Physics

“…The oxygen vacancy (V O ), titanium interstitial (Ti i ), and hydrogen on an interstitial site (H i ) are considered to be potential sources of n-type doping. 10,11,[14][15][16][17][18][19] However, the properties of these donors remain elusive and controversial. The question which of these defects are dominant might furthermore strongly depend on the actual sample treatment.…”

Section: Introductionmentioning

confidence: 99%

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

Zimmermann

Bonkerud

Herklotz

et al. 2018

Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200–700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed.