Surface Magnetism of Cobalt-Doped Anatase TiO2 Nanopowders / 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. // JOURNAL OF PHYSICAL CHEMISTRY C. - 2016. - V. 120, l. 50. - P. 28857-28866.

ISSN/EISSN:

1932-7447 / нет данных

Type:

Article

Abstract:

Cobalt-doped anatase T1-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 T1-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 similar or equal to 1 mu(B) 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.

Author keywords:

ROOM-TEMPERATURE FERROMAGNETISM; T-C FERROMAGNETISM; PHOTOCATALYTIC ACTIVITY; TOPOLOGICAL INSULATORS; PHASE-TRANSFORMATION; OXYGEN VACANCY; UNDOPED TIO2; THIN-FILMS; HYDROPHILICITY; NANOPARTICLES

DOI:

10.1021/acs.jpcc.6b10417

Web of Science ID:

ISI:000390735600053

Соавторы в МНС:

Другие поля

Поле	Значение
Month	DEC 22
Publisher	AMER CHEMICAL SOC
Address	1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Language	English
Keywords-Plus	ROOM-TEMPERATURE FERROMAGNETISM; T-C FERROMAGNETISM; PHOTOCATALYTIC ACTIVITY; TOPOLOGICAL INSULATORS; PHASE-TRANSFORMATION; OXYGEN VACANCY; UNDOPED TIO2; THIN-FILMS; HYDROPHILICITY; NANOPARTICLES
Research-Areas	Chemistry; Science \& Technology - Other Topics; Materials Science
Web-of-Science-Categories	Chemistry, Physical; Nanoscience \& Nanotechnology; Materials Science, Multidisciplinary
Author-Email	galakhov@ifmlrs.uran.ru
ResearcherID-Numbers	Mesilov, Vitaly/J-4256-2013 Gubkin, Andrey/J-3240-2013 Alexander, Korolev/K-3036-2013 Uimin, Mikhail/K-1319-2013 Galakhov, Vadim/J-6030-2013 Yermakov, Anatoly/J-5185-2013 Minin, Artem/L-6957-2016 Svyazhin, Artem/J-4324-2013
ORCID-Numbers	Mesilov, Vitaly/0000-0002-1084-2725 Gubkin, Andrey/0000-0002-4280-7561 Alexander, Korolev/0000-0002-5104-3997 Uimin, Mikhail/0000-0003-3906-8101 Galakhov, Vadim/0000-0002-1642-7362 Yermakov, Anatoly/0000-0001-6466-7064 Minin, Artem/0000-0003-3305-3195 Svyazhin, Artem/0000-0002-6959-5036
Funding-Acknowledgement	Russian Scientific Foundation {[}16-12-10004]
Funding-Text	This work was supported by the Russian Scientific Foundation, Grant No. 16-12-10004. We are grateful to Dr. N. N. Schegoleva for help and useful comments.
Number-of-Cited-References	46
Usage-Count-Last-180-days	10
Usage-Count-Since-2013	17
Journal-ISO	J. Phys. Chem. C
Doc-Delivery-Number	EG0PV