Please use this identifier to cite or link to this item: https://elar.usfeu.ru/handle/123456789/8936
Title: Surface magnetism of cobalt-doped anatase TiO2 nanopowders
Authors: Yermakov, A. Ye.
Zakharova, G. S.
Uimin, M. A.
Kuznetsov, M. V.
Molochnikov, L. S.
Konev, S. F.
Konev, A. S.
Minin, A. S.
Mesilov, V. V.
Galakhov, V. R.
Volegov, A. S.
Korolyov, A. V.
Gubkin, A. F.
Murzakayev, A. M.
Svyazhin, A. D.
Melanin, K. V.
Issue Date: 2016
Publisher: American Chemical Society
Citation: Yermakov, A. Ye. Surface magnetism of cobalt-doped anatase TiO2 nanopowders / A. Ye. Yermakov, G. S. Zakharova, M. A. Uimin [et al.] // Journal of Physical Chemistry C. – 2016. – Vol. 120. – Iss. 50. – P. 28857-28866.
Abstract: Cobalt-doped anatase Ti1−xCoxO2 (0 < x ≤ 0.04) nanopowders (with a particle size of 30−40 nm) were produced by the hydrothermal synthesis method. Morphology, structure, and thermal stability of the synthesized compounds were examined using transmission electron microscopy, infrared spectroscopy, and X-ray diffraction analysis. Using X-ray photoelectron spectroscopy, cobalt ions are shown to have an oxidation state of 2+, with titanium ions having a tetravalent state of Ti4+. In the as-prepared state, all investigated compounds of Ti1−xCoxO2 are paramagnetic, with the value of paramagnetic susceptibility growing in proportion to cobalt content; with the spin of cobalt ion equal to S = 3/2. Analysis of the electron paramagnetic resonance spectra reveals that doping TiO2 with cobalt (up to 2%) is accompanied by a significant increase in the concentration of F+ centers. Further growth of the cobalt content results in a relatively wide line (nearly 600 Oe) in the spectrum, with a g-factor of about 2.005, demonstrating exchange-coupled regions being formed, the fraction of which increases with cobalt content, while the intensity of F+-center signals is reduced appreciably. Annealing of Ti0.96Co0.04O2 in vacuum at 1000 K is shown to have resulted in the substantial localization of cobalt atoms in the subsurface layers, resulting in an approximately 3-fold increase in the Co atoms content on the surface of nanoparticles as compared with that in the bulk. This is shown to be accompanied by appearance of spontaneous magnetization at room temperature, the value of which depends on the cobalt content in TiO2 nanopowders. The value of magnetic moment per Co atom decreases monotonically down to a value of ≃1 μB with cobalt content increasing. A core−shell model proposed to be the most adequate for describing the magnetic properties of TiO2:Co after the reducing annealing. A hypothesis is put forward suggesting that the defect surface enriched with Co atoms and vacancies is described with itinerant type magnetism, allowing for the delocalized nature of electrons near vacancies. © 2016 American Chemical Society.
Keywords: ATOMS
COBALT
COBALT DEPOSITS
ELECTRON SPIN RESONANCE SPECTROSCOPY
HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY
HYDROTHERMAL SYNTHESIS
INFRARED SPECTROSCOPY
IONS
MAGNETIC MOMENTS
MAGNETIC RESONANCE
MAGNETISM
NANOSTRUCTURED MATERIALS
PARAMAGNETIC RESONANCE
PARAMAGNETISM
PARTICLE SIZE
SPECTRUM ANALYSIS
SURFACE DEFECTS
THERMODYNAMIC STABILITY
TITANIUM COMPOUNDS
TITANIUM DIOXIDE
TRANSMISSION ELECTRON MICROSCOPY
X RAY DIFFRACTION ANALYSIS
COBALT DOPED ANATASE
ELECTRON PARAMAGNETIC RESONANCE SPECTRUM
EXCHANGE COUPLED
PARAMAGNETIC SUSCEPTIBILITY
SPONTANEOUS MAGNETIZATION
SUBSURFACE LAYER
SURFACE MAGNETISM
TETRAVALENT STATE
X RAY PHOTOELECTRON SPECTROSCOPY
URI: https://elar.usfeu.ru/handle/123456789/8936
DOI: 10.1021/acs.jpcc.6b10417
SCOPUS: 2-s2.0-85021649468
WoS: WOS:000390735600053
RSCI: 29709707
Appears in Collections:Научные публикации, проиндексированные в SCOPUS и WoS CC

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