Roman Chernikov

Brookhaven National Laboratory · National Synchrotron Light Source II

P65 is a new X-ray Absorption Fine Structure (XAFS) spectroscopy beamline at the high brilliance storage ring PETRA III in Hamburg, Germany. It is providing a mm sized beam and a monochromatic photon flux of up to 10¹² s⁻¹ at 9 keV. The beamline design is optimised for standard EXAFS measurements under ex- and in-situ conditions. The performance of...

X-ray mirrors with sagittal curvature are often used at X-ray beamlines to focus or collimate the beam horizontally. However, if placed in front of a monochromator, the vertical beam divergence introduced by such mirrors can significantly decrease energy resolution and make the beamline more sensitive to misalignment. Such is the case of BioXAS-Sid...

Thermochromic phase transition was studied in CuMoO4 using the Cu and Mo K-edge x-ray absorption spec-troscopy in the temperature range of 10–300 K. The hysteretic behavior has been evidenced from the tempera-ture dependence of the pre-edge shoulder intensity at the Mo K-edge, indicating that the transition from brown-ish-red γ-CuMoO4 to green α-Cu...

To investigate the interplay between electronic structure and itinerant magnetism, Ca1?xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All the samples crystalize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formati...

The pressure effect on the europium valence state was investigated by means of X-ray absorption spectroscopy in the series of samples based on the EuCo2As2 compound. The pressure dependence of the europium valence was obtained in a wide range of applied and chemical pressures; the latter was reached by substituting Ca for Eu. The correlation betwee...

Complex oxides of the Ln2 Hf2 O7 (Ln = lanthanide) series undergo a fluorite to pyrochlore phase transformation. We have studied the whole process of the crystal and local atomic structure realignment during the crystallization and the phase transition in the series of Ln2 Hf2 O7 (Ln = La-Lu) samples synthesized by the coprecipitation method with t...

Intermetallic Ln2Co12As7 (Ln: Y, Ce—Yb) and Ca2Co12As7 are prepared by solid state reaction of the elements using excess Bi as a flux (evacuated silica tubes,1223 K, 8 d).

We present a new implementation of the XAFSmass program that calculates the optimal mass of XAFS samples. It has several improvements as compared to the old Windows based program XAFSmass: 1) it is truly platform independent, as provided by Python language, 2) it has an improved parser of chemical formulas that enables parentheses and nested inclus...

First fast EXAFS spectra have been successfully measured at the Hard X-ray Micro-probe Beamline P06 (PETRA III) synchronously scanning the U32 undulator gap and the monochromator Bragg axis. Stability and spatial homogeneity of the beam are proved to be the limiting factors for the quality of the EXAFS spectra, whereas the performance of the data a...

We report the high-pressure XANES study of the electronic phase transition from 4f7 to 4f 6 configuration of europium in the rare-earth compound EuCu2Ge2. The hydrostatic pressure dependence of the europium valence was obtained in a wide pressure range (1-30 GPa) at room temperature. It was found that upon the pressure increase above 20 GPa the eur...

The process of Tb2Hf2O7 nanocrystals formation upon annealing to 1600°C was investigated by means of X-ray absorption fine structure (XAFS) spectroscopy combined with X-ray diffraction (XRD) and pair distribution function (PDF) analysis. The structure ordering and the growth of nanocrystals upon annealing were estimated independently from XRD patte...

We demonstrate that the action of physical pressure, chemical compression, or aliovalent substitution in ACo2As2 (A = Eu, Ca) has a general consequence of causing these antiferromagnetic materials to become ferromagnets. In all cases, the mixed valence triggered at the electropositive A site results in the increase of the Co 3d density of states at...

We present a new implementation of the XAFSmass program that calculates the optimal mass of XAFS samples. It has several improvements as compared to the old Windows based program XAFSmass: 1) it is truly platform independent, as provided by Python language, 2) it has an improved parser of chemical formulas that enables parentheses and nested inclus...

We report the high-pressure XANES study of the electronic phase transition from 4f$^7$ to 4f$^6$ configuration of europium in the rare-earth compound EuCu$_2$Ge$_2$. The hydrostatic pressure dependence of the europium valence was obtained in a wide pressure range (1-30 GPa) at room temperature. It was found that upon the pressure increase above 20...

We report the high-pressure XANES study of europium intermediate valence in the rare-earth compound Euu2Ge2. The hydrostatic pressure-dependence of europium valence was obtained in a wide pressure range (1-30 GPa) at room temperature. The saturation region of the europium valence was found at the pressure higher than 20 GPa, when the valence reache...

Ternary intermetallics, A2Co12As7 (A=Ca, Y, Ce–Yb), have been synthesized by annealing mixtures of elements in molten Bi at 1223 K. The materials obtained crystallize in the P63/m variant of the Zr2Fe12P7 structure type. The unit cell volume shows a monotonic decrease with the increasing atomic number of the rare-earth metal, with the exception of...

We present an open source python based ray tracing tool that offers several useful features in graphical presentation, material properties, advanced calculations of synchrotron sources, implementation of diffractive and refractive elements, complex (also closed) surfaces and multiprocessing. The package has many usage examples which are supplied to...

Four rare-earth cobalt arsenides, RCo2As2 (R = La, Ce, Pr, Nd), were obtained by reactions of constituent elements in molten Bi. The use of Bi flux also allowed the growth of representative single crystals. All compounds are isostructural and belong to the ThCr2Si2 type (space group I4/mmm). The formation of Co vacancies is observed in all structur...

Temperature-dependent X-ray absorption spectra of the hole-doped La2−x Sr x CuO4 and electron-doped Nd2−x Ce x CuO4−δ high-temperature superconductors were investigated above the Cu K absorption edge. We observed strong anharmonicity in the superconductive CuO2 plane. For x=0.15 it was shown that part of oxygen ions oscillate in a double-well poten...

The experimental X-ray absorption data on the recently prepared magnetic arsenides RCo2As2 (R = rare earth) are provided. The oxidation state of rare-earth ions is explored by means of the X-ray absorption near edge structure (XANES) spectroscopy. Ce and Eu exhibit the intermediate valence state. The rare-earth valence instability sensitive to exte...

A combination of modern locally sensitive methods of structure analysis based on the interaction of synchrotron radiation with condensed matter was used to study the formation and evolution of crystal structures, change in the size of crystallites, the type and degree of cationic ordering, and features of the local atomic structures of compounds Ln...

The parameters of the local crystal structure of dodecaborides RB12 (R = Ho, Er, Tm, Yb, Lu) have been determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the vibrations of the rare-earth ion with respect to the boron cage are well described in the harmonic approximation. At the same time, the displac...

The nanoscopic magneto-electronic phase separation in doped La1-xSrxCoO3 perovskites was studied with local probes. The phase separation is directly observed by M\"ossbauer spectroscopy in the studied doping range of 0.05 <= x <= 0.25 both at room-temperature as well as in the low temperature magnetic phase. Extended with current synchrotron based...

The temperature-dependent extended X-ray absorption fine structure (EXAFS) spectra of hole- and electron-doped high-temperature superconductors (La2 − x Srx CuO4 and Nd2 − x Cex CuO4 − δ, respectively) are investigated above the CuK absorption edge. It is demonstrated that, for superconducting compounds (x = 0.15), the part of the oxygen ions in th...

Ni:a-C:H thin films obtained by reactive sputtering processes were investigated using EXAFS and subsequent wavelet analysis. Depending on overall thin film deposition conditions, the clusters of Ni in Ni:a-C:H can appear as fcc-Ni or as a non-fcc-Ni phase, such as hcp-Ni or Ni3C. While hcp-Ni and Ni3C are hardly distinguishable by XRD, the EXAFS an...

The features of long-range crystal structure and local environment of Ni and Cu atoms in shape memory alloy Ti50Ni25Cu25 are investigated using X-ray diffraction and extended X-ray absorption fine structure spectroscopy (EXAFS) in the temperature range of direct and reverse martensitic transformations. According to XRD study, alloy has the B2 type...

The rearrangement of cerium and lutetium local environment in Ce2Fe17-xMnx and Lu2Fe17-xMnx intermetallics vs. Mn concentration and temperature was investigated by means of the extended X-ray absorption fine structure (EXAFS) spectroscopy above K-Ce absorption edge and powder X-ray diffraction. The valence state of Ce in Ce2Fe17-xMnx was also studi...

A detailed combined study of local electronic and crystal structures was performed for a series of rare-earth cobalt phosphides RCo2P2 (R = La, Ce, Pr, Nd, Eu) with peculiar itinerant magnetic ordering schemes using different methods employing the synchrotron radiation: RIXS, XANES and EXAFS. Europium and cerium are shown to be in the intermediate...

Evolution of the nanocrystalline structure of the complex oxide Dy2HfO5 in the course of thermal annealing at temperatures to 1600°C has been studied by a combination of X�ray and synchrotron methods, including traditional and anomalous X�ray diffraction, PDF, EXAFS, and SAXS. The changes in crystallite size upon annealing of the as�synthesized amo...

Evolution of the nanocrystalline structure of the complex oxide Dy2HfO5 in the course of thermal annealing at temperatures to 1600°C has been studied by a combination of X-ray and synchrotron methods, including traditional and anomalous X-ray diffraction, PDF, EXAFS, and SAXS. The changes in crystallite size upon annealing of the as-synthesized amo...

The process of double oxide Dy2O3-HfO2 nanocrystallites formation upon annealing to 1600°C was investigated with the combination off few X-ray and synchrotron methods. XRD and PDF show the mean crystal structure to be fluorite typical for the compounds of Ln2O3-MeO2 type. The ordering of structure and the growth of nanocrystallites upon annealing w...

Knowledge of the local structure around rare earth elements (REE) in aluminosilicate melts is of great interest for the geochemistry of magmatic processes, particularly for understanding the partitioning of REE between melt and the coexisting crystals in a more comprehensive way. Several studies already proposed a significant influence of the melt...

Reactions between the complexes M3(dpa)4Cl2 (M = Co, Ni; dpa = 2,2′-dipyridylamine), which contain linear trimetallic fragments, and (Bu4N)3[M′(CN)6] (M′ = Fe, Co) result in the formation of CN-bridged coordination polymers. The analysis of the products obtained suggests that they have a two-dimensional structure, in which ditopic [M3(dpa)4]2+ link...

The features of near-edge structure around the L 3-Eu absorption edge are investigated in EuCo2P2, Pr1 − x Eux Co2P2 (x = 0.2, 0.4), and Nd0.6Eu0.4Co2P2 by means of resonant inelastic X-ray scattering (RIXS). Europium is shown to be in the intermediate valence state in all compounds. A comparison is made of the values of europium intermediate valen...

Local and crystalline structures of as-cast SmCo5+/-x alloys subjected to various heat treatments were studied using EXAFS, X-ray diffraction, and metallographic analyses. XRD and EXAFS analyses of SmCo5-x alloys show the evidence of the Sm-enrichment of the SmCo5 phase. The behavior of the lattice parameters of SmCo5 phase in Sm-rich alloys during...

The structural environment around Y in silicate and aluminosilicate glasses containing 5000 ppm Y was investigated as a function of melt composition and polymerization using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The used glass compositions were taken from Prowatke and Klemme (2005) varying in the aluminum saturation index (...

For the first time the rearrangement of cerium local environment in Ce 2 Fe 17−x Mn x (x = 0; 1; 2) intermetallics vs. Mn concentration and temperature was investigated by the spectroscopy of extended X-ray absorption fine structure (EXAFS) above K-Ce absorption edge. At the same time under similar conditions by the spectroscopy of X-ray absorption...

It is generally accepted that the partitioning of trace elements is controlled by temperature, pressure and crystal chemistry (e.g. [1]). However, among others, the results of Prowatke & Klemme [2] on trace element partition-ing between melt and titanite, which varied over several orders of magnitude, suggest strong effects of the melt composition...

Knowledge on the local structure around rare earth elements (REE) in aluminosilicate melts is of great interest for the geochemistry of magmatic processes, particularly for understanding the partitioning of REE between melt and coexisting crystals in a more comprehensive way ([1],[2]). However, the high-temperature (HT) local structure around REE i...

It is generally accepted that the partitioning of trace elements (TE) is controlled by T, P, and crystal chemistry (e.g. [1]). Several studies have also reported a significant influence of the melt composition and thus melt structure on TE partitioning [2 – 4]. Particularly, Prowatke & Klemme's results [4] on TE partitioning between melt and titani...

The formation of (Ln3+)2(M4+)2O7 (Ln = Gd, Dy; M = Zr, Hf) nanocrystallites obtained by annealing mixed hydroxides LnM(OH)7 · nH2O (precursors) synthesized by coprecipitation has been studied by synchronous thermal analysis, X-ray diffraction (normal and anomalous diffraction of synchrotron radiation), and EXAFS. In the systems under consideration,...

It has been established that the process of producing the Ln2 + x Me2 − x O7 − x/2 (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration...

The rearrangement of the local environment of cerium has been examined using extended X-ray absorption fine structure spectroscopy above the K-Ce absorption edge for various manganese contents and temperatures in Ce2Fe17 − x Mnx intermetallics (x = 0, 1, 2). The valence state of cerium has been studied simultaneously by X-ray absorption near-edge s...

The effective valence of cerium is studied by L 3-XANES spectroscopy using synchrotron radiation in the following valence-unstable systems with different types of magnetic ordering: a CeNi matrix doped with neodymium, praseodymium, and gadolinium ions in the temperature range 5–300 K and the Ce2Fe17 − x Mnx intermetallic compound. The obtained depe...

Pr0.8M0.2Co2P2 (M: Eu, Ca) are synthesized from mixtures of the elements in a Sn flux (silica ampules, 1155 K, 10 d) and characterized by powder and single crystal XRD, Moessbauer spectroscopy, magnetic measurements, and DFT band structure calculations.

The extended X-ray absorption fine structure spectroscopy (EXAFS) was applied to investigate the local structure peculiarities of TiNi-based shape memory alloys Ti50Ni25Cu25 and Ti39.2Ni24.8Cu25Hf11. The phase composition of ternary alloy was examined with the additional X-ray diffraction. Our experimental results demonstrate that the most signific...

Results of hard magnetic Fe-Ni-Al alloys after various thermal processing local structure researches by method of EXAFS-spectroscopy with use of synchrotron radiation at temperature 77 K are presented. It is established, that during cooling a firm solution with critical speed reorganization of a local environment of nickel relative to quickly tempe...

It is generally accepted that the partitioning of trace elements (TE) is controlled by T, P, and crystal chemistry (e.g. [1]). Several studies have also reported a significant influence of the melt composition and thus melt structure on TE partitioning [2 – 4]. Particularly, Prowatke & Klemme's results [4] on TE partitioning between melt and titani...

Trace elements are important indicators in magmatic and metamorphic rock on Earth, Moon and the terrestrial planets. It is generally accepted that the partitioning of trace elements (TE) is controlled by T, P, crystal chemistry and melt composition (e.g. [1]). Particularly, the trace element partition coefficients of Prowatke and Klemme's [2] betwe...

The cerium effective valence was investigated by means of CeL(3)-XANES spectroscopy in some intermediate valence Ce-based systems with different magnetic ordering mechanisms: CeNi doped with Nd, Pr and Gd in the temperature range 5-300 K, and Ce(2)Fe(17-x)Mn(x) intermetallics. The dependences obtained are considered within the frames of generally a...

Temperature dependent comparative EXAFS studies of Ba1-xKxBiO3 superconducting oxides and copper based superconductors with hole (La2-xSrxCuO4) and electron (Nd2-xCexCuO4-delta) doping showed the common dynamical local structure nonuniformity observed as the double-well potential of oxygen ion oscillations. Obtained data evidence that these local s...

The extended X-ray absorption fine structure spectroscopy (EXAFS) was applied to investigate the local structure peculiarities of TiNi-based shape memory alloys Ti(50)Ni(25)Cu(25) and Ti(39.2)Ni(24.8)Cu(25)Hf(11). Our experimental results demonstrate that the most significant changes in local crystalline structure under martensitic transformation a...

Heat capacity measurements of amorphous and crystallized R16.7Ni83.3 (RNi5) samples (RNi5) (R = La, Pr) in magnetic fields were performed, along with measurements of the average interatomic Ni–Ni distances and average square deviations from the interatomic distances. Changes were observed in the interatomic distances in La16.7Ni83.3, and in the ele...

X-ray absorption spectra of the oxide systems Nd2-xCexCuO4-δ (NCCO) above the K-Cu absorption edge were investigated in temperature range 4 ÷ 300 K. It is assumed that oxygen ions in superconductive CuO2 plane move in a double-well potential similarly to abnormal oxygen vibrations uncovered earlier in superconductive systems Ba1-xKxBiO3 and La2-xSr...

Local crystalline structure of hypo- and hyperstoichiometric SmCox alloys with x = 5.15, 4.95, 4.0, 3.75 heat treated in different conditions was investigated by means of the X-ray absorption spectroscopy. Experimental spectra were measured above the L3-Sm absorption edge. EXAFS-analysis shows that stacking faults appear in hyperstoichiometric allo...

Results of Hall effect measurements are reported both below and above the threshold electric field, E(t), for depinning the low temperature charge density wave (CDW) in NbSe(3) in a wide temperature range. At low electric fields, below E(t), we have observed a change in the sign of the Hall voltage at all temperatures lower than T(p2). Comparison b...

We report the results of detailed investigations of Hall effect in NbSe3 under magnetic fields up to B = 9T. We show that the Hall voltage, V-H, changes sign in a wide temperature range and that the magnetic field for which V-H crosses zero is temperature dependent. We demonstrate that in high magnetic field the CDW motion changes significantly the...

The effect of dispersivity on the local-structure features in ZrN nanocrystals has been investigated by X-ray absorption (EXAFS) spectroscopy. The Debye-Waller factors and bond lengths have been determined for Zr-N and Zr-Zr coordination spheres. It is found that a decrease in the nanoparticle size leads to an increase in the static Debye-Waller fa...

The local structure of the electron-doped high-temperature superconductor Nd2 − x Ce x CuO4 + δ has been investigated by EXAFS spectroscopy using synchrotron radiation in the temperature range 5–300 K. The radii, coordination numbers, and Debye-Waller factors of the nearest coordination spheres of the copper, neodymium, and cerium local environment...

The character of transformation of the local environment of zirconium and palladium atoms in Zr70Pd30 binary alloy at a transition from the amorphous state to the quasicrystalline and crystalline states and in Zr70Be30 and Zr80Pt20 binary alloys at a transition from the amorphous to the quasicrystalline state have been investigated by extended X-ra...

The rearrangements of the local environment of zirconium and palladium atoms in the binary alloy Zr{sub 70}Pd{sub 30} upon the transformation from the crystalline to the quasicrystalline and amorphous states were studied by extended X-ray absorption fine structure (EXAFS) analysis. In the quasicrystalline phase, the icosahedral environment was foun...

The particular features of the local electronic and local crystal structures of the mixed-valence compound Sm1 − x Y x S are studied by the XAFS spectroscopy methods in the temperature range 20–300 K for the yttrium concentration x = 0.17, 0.25, 0.33, and 0.45. The temperature behavior of the valence of Sm, as well as of the lengths and the Debye-W...

On the basis of the investigation of the temperature dependences of EXAFS spectra of the Ba1−x K x BiO3 superconducting oxide, a model of relationship between the local crystalline and electronic structures is proposed. It is found that oxygen ions vibrate in a double-well potential and their vibrations are correlated with the local electron pair t...

The valence state of samarium and the local environments of samarium and yttrium ions in the intermediatevalence compound Sm1−x Y x S (x = 0.17, 0.25, 0.33, or 0.45) are studied over a wide temperature range of 20–300 K using x-ray absorption spectroscopy. The temperature dependence of Sm-S, Sm-Sm(Y), Y-S, and Y-Sm(Y) bond lengths and the Debye-Wal...

Mixed-valence phenomena occurring in the “black” (B) and “gold” (G) phases of Sm1−xYxS have been studied by x-ray diffraction, x-ray absorption spectroscopy, and inelastic neutron scattering. Lattice-constant and phonon-dispersion results confirm that the valence instability occurs already inside the B phase. On the other hand, pronounced temperatu...

Contribution to a conf. proceeding (book/online)

X-ray absorption spectrum of the Sm L-3 edge have been measured in the intermediate valence Sm1-xYxS for two dopant concentrations x = 0.33 and 0.45. From the analysis of near-edge structure using the method that takes into consideration multiple scattering effects we managed to specify Sm valence value more precisely in wide temperature interval....

We report the results of the intermediate valence compound EuCu 2Si 2 local electron and crystalline structure studies by means of L 3-Eu XANES and K-Cu EXAFS spectroscopy. Temperature dependence of the europium valence has been defined. In EXAFS studies, we have analyzed Cu atoms local environment and have revealed bond length and rigidity paramet...

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)

Contribution to a conf. proceeding (book/online)