1. A.T. Kozakov, A.G. Kochur, K.A. Googlev, A.V. Nikolsky, I.P. Raevski, V.G. Smotrakov,
V. V. Eremkin X-RAY PHOTOELECTRON STUDY OF THE VALENCE STATE OF
IRON IN IRON _ CONTAINING SINGLE CRYSTAL (BiFeO3, PbFe1/2Nb1/2O3), AND
CERAMIC (BaFe1/2Nb1/2O3) MULTIFERROICS // J. Electron Spectroscopy and Related
Phenomena, V.184 , P.16 -23 , 2011
Abstract
Fe2p, Fe3p, and Fe3s X-ray photoelectron spectra (XPS) are measured with high resolution in
single-crystal multiferroics BiFeO3 and PbFe1/2Nb1/2O3, as well as in reference samples Fe2O3,
FeSO47H20, FeC2O42H2O. The spectra are assigned based on an isolated-ion
approximation calculation. Single-crystal multiferroics and Fe2O3 are shown to have the Fe
ions only in the Fe3+ valence state. Ceramic samples of BaFe1/2Nb1/2O3 with various relative
Fe2+/Fe3+ abundances are synthesized in various conditions. An approximate method to
determine the Fe2+/Fe3+ ratio in a sample is suggested. The method is based on the fitting of
the sample’s 2p XPS with a superposition of Fe2+ and Fe3+ 2p spectra. An effect of
temperature regimes of sintering and annealing on the Fe2+/Fe3+ ratio is demonstrated.
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2. A.T. Kozakov, A.G. Kochur, A.V.Nicolsky, K.A. Googlev, V.G.Smotrakov, V.V.Eremkin.
VALENCE AND MMAGNETIC STATE OF TRANSITION – METAL AND RARE –
EARTH IONS IN SINGLE – CRYSTAL MULTIFERROICS RMn2O5 (R = Y, Bi, Eu,
Gd) FROM X-RAY PHOTOELECTRON SPECTROSCOPY DATE // Journal of
Electron Spectroscopy and Related Phenomena V. 184, P. 508 – 516, 2011
Abstract
Single crystals of orthorhombic multiferroics RMn2O5 (R = Y, Bi, Eu, Gd) , and hexagonal manganite
YMnO3 are grown. X-ray photoelectron spectra of the core levels of the Mn, Bi, Y, Eu, Gd, and O
atoms in multiferroics are obtained at room temperatute with the ESCALAB 250 microprobe system
with monochromatization of the exiting X-tay radiation. X-ray photoelectron spectra of Mn2p, Mn3s,
R4s, and R4d (R=Eu, Gd) levels are assigned based on one – configuration isolated – ion
approximation calculations with taking the temperature effect into account. It is shown using the
photoelectron spectroscopy methods that both Mn3+ and Mn4+ ions are present in orthorhombic
multiferroics, while Eu and Gd are in trivalent state. Paramagnetic moments per structural unit are
calculated and compared with those determined from our spectroscopic date and with the date from
other authors.
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3. A.G. Kochur, A.T. Kozakov, A.V. Nikolskii, K.A. Googlev, A.V. Pavlenko, I.A.
Verbenko, L.A. Reznichenko, T.I. Krasnenko VALENCE STATE OF THE MANGANESE
IONS IN MIXED – VALENCE La1-ά BiβMn1-γO3+δ CERAMICS BY Mn 2p AND Mn 3s
X-RAY PHOTOELECTRON SPECTRA // Journal of Electron Spectroscopy and Related
Phenomena V. 185 P. 175– 183 , 2012
Abstract
Valence state of Mn in La1-BiMn1+O3 (LBMO) ceramic samples and in orthorhombic
manganates RMn2O5 (R = Y, Bi, Eu, Gd), is studied using Mn2p- and Mn 3s-spectra. Both
Mn3+ and Mn4+ ions are shown to be present in those compounds. Relative Mn3+/Mn4+ ions
contents are determined by fitting experimental Mn2p-spectra with weighted superpositions
of theoretical spectra of Mn3+ and Mn4+ ions calculated in one-configuration Pauli-Fock
approximation considering thermal excitations in initial state. Content of the Mn4+ ions
correlates with the deviation  in La1-BiMn1+O3 from stoichiometry, La1-xBixMnO3.
Separation of low-spin and high-spin components of Mn3s-spectrum can be sensible to the
relative content of Mn3+ and Mn4+ ions. Mn3+/Mn4+ ratios derived from Mn2p- and from
Mn3s-spectra compare well in the case of the RMn2O5 manganates, while in the case of the
LBMO ceramics the results obtained from the Mn3s spectra are physically meaningless. Due
to a complex interplay between 3d-electrons delocalization and strong many-electron effects
the 3s spectra of 3d-elements may be misleading.
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4. A.T. Kozakov, A.G. Kochur, L.A. Reznichenko , L.A. Shilkina, A.V. Pavlenko, A.V.
Nikolskii, K.A. Googlev, V.G. Smotrakov SINGLE – CRYSTAL RARE – EARTHS
MANGANITES La1-x-yBix AyMnαO3± (A = Ba,Pb): CRYSTAL STRUCTURE,
COMPOSITION, AND Mn IONS VALENCE STATE. X-RAY DIFFRACTION AND
XPS STUDY // Journal of Electron Spectroscopy and Related Phenomena V. 186 P. 14-24
2013
Abstract
Single crystals of La1-xBixMnαO3± и La1-x-yBix AyMnαO3± (A = Ba, Pb) are grown, their
crystal and electron structure is studied. Relative Mn3+/Mn4+ abundance in each single crystal
is determined via fitting experimental Mn2p-spectra with weighted superposition of
theoretical spectra of tri- and quadrivalent Mn, and, for barium-free samples, from energy
splitting of the Mn3s-spectra components. Strong heterogeneousness of the crystals both in
elemental composition and crystal structure is discovered. It is shown that the
heterogeneousness displays itself in various oxygenic environments around Mn atoms which
give rise to the appearance of Mn4+ ions. A simple model is proposed that allows
understanding the nature of the appearance of Mn4+ ions in single crystals of lanthanumbismuth manganites.
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5. A.T. Kozakov, O.E. Polozhentsev, A.V. Soldatov, K.A. Googlev, I.P. Raevski, A.V.
Nikolsky X-RAY PHOTOELECTRON STUDY AND FIRST PRINCIPLE
CALCULATIONS OF THE ELECTRONIC STRUCTURE OF PbFe1/2Nb1/2O3
SINGLE – CRYSTAL IN THE FERROELECTRIC AND PARAELECTRIC PHASES
// J.Alloys and Compounds. V. 579, P. 401-405, 2013
X-ray photoelectron study using ESCALAB 250 and first principle calculations using
the FEFF9 method have been carried out for the electronic structure of single crystal of
PbFe1/2Nb1/2O3 multiferroic in the rhombohedral (296 K) and tetragonal (368 K) ferroelectric
and cubic paraelectric (403 K) phases. The shift of the energy of Pb6s-maximum in the
valence band due to the ferroelectric-paraelectric phase transition predicted by first principle
calculations was observed experimentally.
6. N. Kumar, Radhika Ramadoss, A.T. Kozakov, K.J. Sankaran, S. Dash, A.K. Tyagi, N.
H.
Tai,
I-Nan
Lin HUMIDITY
DEPENDET
FRICTION
MECHANISM
IN
ULTRANANOCRYSTALLINE DIAMOND FILM // J. Phys. D. :Applied Phys. V. 46, P.
275501 (8 pp), 2013
Abstract
Friction behavior of ultrananocrystalline diamond (UNCD) film deposited by microwave
plasma enhanced chemical vapor deposition (MPECVD) technique is carried out in controlled
humid atmosphere. The value of friction coefficient consistently decreases while increasing
the humidity level during the tribology test. This value is 0.13 in 10% relative humid
conditions which is significantly decreased to 0.004 in 80% relative humid conditions. Such a
reduction in friction coefficient is ascribed to passivation of dangling covalent bonds of
carbon atoms which occurs due to formation of chemical species of hydroxyl and carboxylic
groups such as C–COO, CH3COH and CH2–O bonding states.