O. Khyzhun | Frantsevich Institute for Problems of Materials Science, NAS of Ukraine (original) (raw)

Papers by O. Khyzhun

Bulletin of the Russian Academy of Sciences: Physics, 2009

The modification of polished (001) surfaces of potassium titanyl arsenate, KTiOAsO 4 (KTA) by 1.5... more The modification of polished (001) surfaces of potassium titanyl arsenate, KTiOAsO 4 (KTA) by 1.5 keV Ar + ion irradiation has been investigated using reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS).

Modification of mechanically polished KY(WO 4 ) 2 (010) crystal surface by Ar + , 1.5 keV, ion bo... more Modification of mechanically polished KY(WO 4 ) 2 (010) crystal surface by Ar + , 1.5 keV, ion bombardment has been studied with reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS).

Journal of Alloys and Compounds

X-Ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) methods were used to... more X-Ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) methods were used to study the electronic structure of rhombohedral Ta 4 C 3 and TaC 0.59 N 0.15 compounds, as well as of several samples of the cubic TaC x N ∼0.8−x system. The XPS valence band spectra and the XES Ta L␤ 5 bands were derived for the rhombohedral compounds, but the Ta L␤ 5 , N K␣ and C K␣ emission bands for the cubic TaC x N ∼0.8−x carbonitrides were studied and compared on a common energy scale. A strong hybridization of the Ta 5d-like and C(N) 2p-like states is characteristic of the compounds of the TaC x N ∼0.8−x system studied, but the hybridization between the C 2p-like and N 2p-like states is absent. The substitution of carbon atoms for nitrogen atoms leads to increasing the metallic and ionic components and decreasing the covalent component of the chemical bonding in both systems studied. However, the metallic component is somewhat higher, but the ionic component is smaller to some degree in the rhombohedral compounds compared with those of cubic TaC x N ∼0.8−x system for specimens possessing similar nitrogen-to-carbon ratios.

Journal of Physics Conference Series

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption sp... more X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were used to study the electronic structure of hexagonal h-WO 3 and h-WO 2.8 nanoparticles. For comparison, nanopowder substoichiometric monoclinic tungsten oxides with close content of oxygen atoms, namely m-WO 3 and m-WO 2.77 compounds, were also investigated. For the mentioned oxides, XPS valence-band and corelevel spectra, XES O K bands and XAS W L III and O 1s edges were derived. The XPS valence-band spectra and O K emission bands in the mentioned hexagonal and monoclinic tungsten oxides were compared on a common energy scale. Both the O K bands and XPS valence-band spectra broaden somewhat in the sequences h-WO 3 h-WO 2.8 and m-WO 3 m-WO 2.77 , with the half-widths of the spectra being somewhat higher for the hexagonal oxides as compared with those for the monoclinic compounds. The effective positive charge state of tungsten atoms in h-WO 2.8 is very close to that in m-WO 2.77 , but the negative charge states of oxygen atoms are close to each other for all the tungsten oxides under consideration.

Direct nitridation synthesis and characterization of Si3N4 nanofibers

Research on Chemical Intermediates, 2015

ABSTRACT Silicon nitride nanofibers were prepared by direct nitridation of silicon powder, with a... more ABSTRACT Silicon nitride nanofibers were prepared by direct nitridation of silicon powder, with an iron catalyst, under nitrogen flow. The as-prepared nanofibers have the α-Si3N4 structure. Micromorphology and phase composition of the as-prepared α-Si3N4 nanofibers were characterized by scanning and transmission electron microscopy and by X-ray diffraction analysis, respectively. The electronic structure of silicon nitride nanofibers was compared with that of Si3N4 powder by X-ray photoelectron spectroscopy and X-ray emission spectroscopy.

Electronic Properties of h-WO3 and CuWO4 Nanocrystalsas Determined from X-ray Spectroscopy and First-Principles Band-Structure Calculations

International Journal of Applied Physics and Mathematics, 2011

... Prof. Khyzhun is a member of Ukrainian Physical Society and Ukrainian Materials Society. Vale... more ... Prof. Khyzhun is a member of Ukrainian Physical Society and Ukrainian Materials Society. Valeriy l. Bekenev, was born in Rostov-on-Don/ Russia on August, 1946. He received the diploma degree in solid state physics from the Rostov-on-Don State University in 1969. ...

Journal of Physics and Chemistry of Solids, 2015

a b s t r a c t β-RbNd(MoO 4 ) 2 microplates have been prepared by the multistage solid state syn... more a b s t r a c t β-RbNd(MoO 4 ) 2 microplates have been prepared by the multistage solid state synthesis method. The phase composition and micromorphology of the final product have been evaluated by XRD and SEM methods. The electronic structure of β-RbNd(MoO 4 ) 2 molybdate has been studied employing the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). For the molybdate, the XPS core-level and valence-band spectra, as well as XES bands representing energy distribution of the Mo 4dand O 2p-like states, have been measured. It has been established that the O 2p-like states contribute mainly to the upper portion of the valence band with also significant contributions throughout the whole valence-band region. The Mo 4D-like states contribute mainly to a lower valence band portion.

Materials Chemistry and Physics, 2012

Materials Research Bulletin, 2010

We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO 4 and ZrTiO... more We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO 4 and ZrTiO 4 . We found that the compressibility of these ceramics is highly non-isotropic, being the b-axis the most compressible one. In addition, the a-axis is found to have a small and negative compressibility. At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition in HfTiO 4 (ZrTiO 4 ), coexisting the low-and high-pressure phases in a broad pressure range. The new high-pressure phase has a monoclinic structure which involves an increase in the Ti-O coordination and a collapse of the cell volume.

Journal of Physical Chemistry C, 2007

The effect of 1.5 keV Ar + ion irradiation on the (001) surfaces of potassium titanyl arsenate, K... more The effect of 1.5 keV Ar + ion irradiation on the (001) surfaces of potassium titanyl arsenate, KTiOAsO 4 (KTA), has been investigated using reflection high-energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). The (001) KTA surface is very sensitive to 1.5 keV Ar + ion irradiation which induces significant structural modification in the top surface layers. The bonds in the KTA crystal lattice are relatively less unstable when compared to ; reduction of As 5+ ions with the formation of As 0 and partial As loss from the top surface occurs with Ar + ion irradiation. The formation of an unstable layer with chemically active and passive arsenic states may be a factor reducing the optical parameters and durability of nonlinear devices involving KTA. Figure 1. The schematic representation of the crystal structure of KTiOAsO4 (KTA) for the (001) plane.

physica status solidi (b), 1998

The X-ray emission spectroscopy (XES) method has been used to study the electronic structure of s... more The X-ray emission spectroscopy (XES) method has been used to study the electronic structure of substoichiometric tantalum mononitrides. Both the Ta Lb 5 and N Ka X-ray emission spectra of cubic nitrides TaN x (NaCl structure, 0.81 x 1.172), hexagonal nitrides TaN 0.99 (CoSn structure) and TaN 0.90 (WC structure) have been derived and compared on a common energy scale. In the sequence TaN (CoSn structure) 3 TaN (WC structure) 3 TaN (NaCl structure) a decrease of the N Ka band halfwidth was observed. In most substoichiometric cubic tantalum mononitrides with vacancies on the metal sublattice (1.134 x 1.172) a subband of non-bonding N 2p-like states appeared in the energy region between the Ta 5d±N 2p-and Ta 5d-like bands. In all tantalum nitrides studied the Ta 5d-like and N 2p-like states are strongly hybridized, and a charge transfer occurs from Ta to N atoms.

Journal of Structural Chemistry, 2011

The TiL α , FeL α and OK α ultrasoft X-ray emission bands obtained in experiment reflect, respect... more The TiL α , FeL α and OK α ultrasoft X-ray emission bands obtained in experiment reflect, respectively, the energy distribution of mainly the Ti3d, Fe3d and O2p electronic states in Ti 4 Fe 2 O compound, which is an efficient hydrogen absorber for energy cells. Full and partial densities of electronic states for all atoms constituting the indicated oxide were calculated by a modified method of associated plane waves (APW) using the WIEN2k software package. The APW calculation data for Ti 4 Fe 2 O compound as well as superposition of TiL α , FeL α and OK α ultrasoft X-ray emission bands on a single energy scale indicate that O2p states in the oxide are localized mainly near the bottom of the valence band, the major contribution near the ceiling of the valence band belonging to Fe3d and Ti3d states. According to the APW calculation, the major contribution to the bottom of Ti 4 Fe 2 O conduction band is made by Fe3d* and Ti3d* states. The APW data for Ti 4 Fe 2 O are supported by the cluster calculation performed for this compound using a FEFF82 software package.

Journal of Physics and Chemistry of Solids, 2013

First-principles band-structure augmented plane wave þlocal orbitals (APWþ LO) calculations as in... more First-principles band-structure augmented plane wave þlocal orbitals (APWþ LO) calculations as incorporated in the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) measurements are performed to elucidate the electronic structure of Zr 4 Fe 2 O oxide, a very prospective hydrogen-storage material. Total and partial densities of states for Zr 4 Fe 2 O are derived from the APW þ LO calculations. The XPS valence-band spectrum as well as the XES Zr Lb 2,15 , Fe L a and O K a bands are measured for Zr 4 Fe 2 O 0.6 oxide. Our APW þ LO calculations show that the O 2plike states make the major contributions at the bottom of the valence band, whilst the Fe 3d-and Zr 4dlike states are the dominant contributors at the top of the valence band and at the bottom of the conduction band of Zr 4 Fe 2 O. Peculiarities of the occupation of the valence band of Zr 4 Fe 2 O predicted by the APW þ LO calculations are confirmed experimentally by comparison, on the common energy scale, of the XPS valence-band spectrum and the XES bands representing the energy distributions of the Zr 4d-, Fe 3d-and O 2p-like states in the compound under consideration. In addition, the XPS Zr 3d, Fe 2p and O 1s core-level binding energies are derived for Zr 4 Fe 2 O 0.6 oxide.

Journal of Materials Science: Materials in Electronics, 2013

Novel materials for the infrared two-photon absorption-Tl 1-x In 1-x Sn x Se 2 single crystals (x... more Novel materials for the infrared two-photon absorption-Tl 1-x In 1-x Sn x Se 2 single crystals (x = 0, 0.1, 0.2, 0.25) were grown. Their optoelectronic properties including two-photon absorption at wavelength equal to 9.4 lm at different temperatures were studied. From the spectral data it was established that band gap energy increases with increasing SnSe 2 content in the solid solutions reaching its maximum for the largest content (x = 0.25). The infrared two photon absorption has achieved its maximal value at x = 0.1. The temperature dependence of the optical band gap at various compositions in the range of 77-300 R is practically linear. The band gap value decreases with the increase of T causing the spectral shift of the absorption edge to the low-energy region.

Journal of Electron Spectroscopy and Related Phenomena, 1996

X-ray photoelectron (XPS), emission (XES), and absorption (XAS) spectroscopy methods have been us... more X-ray photoelectron (XPS), emission (XES), and absorption (XAS) spectroscopy methods have been used to study the electronic structure of cubic TaC x and hexagonal Ta 2 C y (y = 2x) carbides, and also rhombohedral z-Ta 4 C 3 and e-Ta 3 C 2 phases. The XPS core-level binding energies (BEs) and valence-band structures for TaC x over the range 0.36 Յ x Յ 0.98 have been determined. It was established that E f was generally lowered by the introduction of C-vacancies in cubic tantalum carbides. The results of the XPS and XES studies indicate that the layered subcarbides z-Ta 4 C 3 and e-Ta 3 C 2 are individual phases and are by no means a simple mixture of the cubic TaC x and hexagonal Ta 2 C y carbides. In the layered subcarbides z-Ta 4 C 3 and e-Ta 3 C 2 the formation of new (shortened) M-M bonds between the tantalum atoms neighbouring the {111} plane of the carbon sublattice, where the C-vacancies concentrate, results in the appearance of an additional peak (E BE Ϸ 2 eV below E f ) in the XPS valence-band spectra. In the row TaC x → z-Ta 4 C 3 → e-Ta 3 C 2 → Ta 2 C y the XPS Ta 4f and C 2s core-level BEs and main peaks of the XPS valence-band spectra shifted toward the Fermi level by about 0.5 eV, while the C 1s BEs remained constant (within the experimental error) for all studied subcarbides. In this row some shifts of the main maxima of the XES Ta 5d-like and C 2p-like bands toward E f are observed. In all tantalum carbides the charge transfers from Ta atoms to C atoms.

Journal of Electron Spectroscopy and Related Phenomena, 2005

Resonant soft X-ray emission (SXE) spectra have been measured for a series of excitation energies... more Resonant soft X-ray emission (SXE) spectra have been measured for a series of excitation energies at the V L␣ and O K␣ bands of divanadium pentoxide, V 2 O 5 . In addition, a near-edge X-ray absorption fine structure (NEXAFS) spectrum at the V 2p and O 1s edges has been also recorded to aid the assignment of the features seen in the SXE data. The V L␣ SXE spectrum of V 2 O 5 consists of two distinct components that can be assigned to the V 3de g -like states strongly hybridized with the O 2p -like states and to the V 3dt 2g -like states weakly hybridized with the O 2p -like states. The resonant SXE spectra recorded at photon energies close to the position of the V L III edge revealed Raman-like features with an energy loss of 7 eV similar to charge transfer states previously observed by Schmitt et al. , Phys. Rev. B 69 (2004) 125103] for the V 6 O 13 oxide.

The Journal of Chemical Physics, 2008

X-ray emission spectroscopy ͑XES͒ at the O K␣ threshold has been used to investigate the electron... more X-ray emission spectroscopy ͑XES͒ at the O K␣ threshold has been used to investigate the electronic structure of a microporous pure calcined zeolite with the crystal structure of the MFI-type framework ͑silicalite͒, a deboronated MFI zeolite ͑DB-MFI͒, a pure mesoporous cubic MCM-48 material, a MCM-48 loaded with copper and zinc oxide nanoparticles ͑Cu/ ZnO-MCM-48͒, and a crystalline layered silicic acid H-RUB-18. For comparison, the XES O K␣ spectrum of pure ␣-quartz has also been recorded. In the nonresonant energy regime the XES O K␣ spectra for all these compounds look very similar indicating that the electronic structure of the micro-and mesoporous silica materials is very similar to that of quartz. In the resonant regime, however, the spectra exhibit significant differences. In all the materials under study, the resonant XES O K␣ spectra recorded at photon energies close to the positions of the O K edges show Raman-type inelastic peaks with an energy loss of 11 eV, originating from electronic excitations within these insulating materials. The prominent features in the XES O K␣ spectra of ␣-quartz and H-RUB-18 are analyzed by means of quantum chemical ab initio cluster calculations.

Journal of Alloys and Compounds, 2013

We report on calculations of total and partial densities of states of atoms constituting the high... more We report on calculations of total and partial densities of states of atoms constituting the high-temperature (HT) tetragonal Tl 3 PbBr 5 phase (space group P4 1 ) using the full potential linearized augmented plane wave (FP-LAPW) method. Our theoretical data reveal that the tetragonal HT-Tl 3 PbBr 5 phase is an indirect-gap material with band gap of 2.26 eV. In addition, the FP-LAPW calculations render that dominant contributors in the valence-band region of HT-Tl 3 PbBr 5 are the Br 4p-like states, which contribute mainly into the top and the central portion of the valence band with also significant contributions throughout the whole valence-band region. The main contributors to the bottom of the valence band of the HT-Tl 3 PbBr 5 phase are the Tl 6s-like states, whilst the unoccupied Pb 6p-like states dominate at the bottom of the conduction band. The X-ray photoelectron core-level and valence-band spectra for the HT-Tl 3 PbBr 5 phase have been measured and compared with those of previously studied the low-temperature orthorhombic Tl 3 PbBr 5 phase.

Journal of Alloys and Compounds, 2010

Ti4Fe2O Electronic structure Band-structure calculations X-ray photoelectron spectroscopy X-ray e... more Ti4Fe2O Electronic structure Band-structure calculations X-ray photoelectron spectroscopy X-ray emission spectroscopy a b s t r a c t Electronic properties of Ti 4 Fe 2 O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the first-principles band-structure augmented plane wave + local orbitals (APW + LO) method with the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and soft X-ray emission spectroscopy (SXES). Total and partial densities of states of the constituent atoms of Ti 4 Fe 2 O have been derived from the APW + LO calculations. The XPS valence-band spectra as well as the SXES Ti L␣, Fe L␣ and O K␣ bands have been measured for a series of Ti 4 Fe 2 O x oxides (x = 1.0, 0.5, and 0.25). The present APW + LO calculations reveal that, the O 2p-like states are the dominant contributors into the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Ti 4 Fe 2 O are dominated by contributions of the Fe 3d-and Ti 3d-like states. The APW + LO results are confirmed experimentally by a comparison on a common energy scale of the XPS valence-band spectra and the SXES Ti L␣, Fe L␣ and O K␣ bands of the Ti 4 Fe 2 O x oxides. The XPS Ti 2p, Fe 2p and O 1s core-level binding energies have been measured for the compounds under consideration.