Mössbauer spectroscopy evidence of intrinsic non‐stoichiometry in iron telluride single crystals

The FeTe parent compound for iron‐superconductor chalcogenides was studied applying Mössbauer spectroscopy accompanied by ab initio calculations of electric field gradients at the iron nuclei. Room‐temperature (RT) Mössbauer spectra of single crystals have shown asymmetric doublet structure commonly ascribed to contributions of over‐stoichiometric iron or impurity phases. Low‐temperature Mössbauer spectra of the magnetically ordered compound could be well described by four hyperfine‐split sextets, although no other foreign phases different from Fe_1.05Te were detected by XRD and microanalysis within the sensitivity limits of the equipment. Density functional ab initio calculations have shown that over‐stoichiometric iron atoms significantly affect electron charge and spin density up to the second coordination sphere of the iron sub‐lattice, and, as a result, four non‐equivalent groups of iron atoms are formed by their local environment. The resulting four‐group model consistently describes the angular dependence of the single crystals Mössbauer spectra as well as intensity asymmetry of the doublet absorption lines in powdered samples at RT. We suppose that our approach could be extended to the entire class of FeSeTe_x compounds, which contain excess iron atoms.

     

Improved Method for Preparation of 3-(1H-Indol-3-yl)benzofuran-2(3H)-ones

3-(1H-Indol-3-yl)benzofuran-2(3H)-ones were efficiently accessed via polyphosphoric acid-mediated condensation of 3-(2-nitrovinyl)-1H-indoles with phenols.     

Synthesis and Spectroscopic and Luminescent Properties of Er,Yb and Lu Complexes with Cyano-Substituted Phthalocyanine Ligands

Based on 4,4′-[1,3/4-phenilenebis(oxy)]phthalodinitriles, the mixture of phthalocyaninates of various structures with rare-earth metals were obtained by template fusion method minimizing the side polymerization processes. Target monophthalocyaninates were isolated from the reaction mixture and purified using column and then gel permeation chromatography. The compounds were characterized by NMR, IR spectroscopy, mass spectrometry, and elemental analysis. The spectral properties were studied and the aggregation behavior of the synthesized Er, Yb, and Lu phthalocyaninates in chloroform, acetone, and tetrahydrofuran was determined. It has been shown that lutetium complexes with 3,4-dicyanophenoxyphenoxy ligands are the least stable and least resistant to aggregation in solution, while erbium and ytterbium phthalocyaninates proved to be stable in all studied media. The quantum yields and fluorescence lifetimes of the complexes in chloroform and tetrahydrofuran were calculated.     

Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

Ternary potassium-iron sulfide, KFeS₂, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, etc. While some of the measurements can be satisfactorily described, the deficiency of the entropy changes upon the magnetic transition and the spin state of the iron ion remains a challenge for the further understanding of magnetism. In this work, high-quality single-crystalline samples of KFeS₂ were grown by the Bridgman method, and their stoichiometry, crystal structure, and absence of alien magnetic phases were checked, utilizing wave-length dispersive X-ray electron-probe microanalysis, powder X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy, respectively. An ab initio approach was developed to calculate the thermodynamic properties of KFeS₂. The element-specific phonon modes and their density of states (PDOS) were calculated applying the density functional theory in the DFT + U version, which explicitly takes into account the on-site Coulomb repulsion U of electrons and their exchange interaction J. The necessary calibration of the frequency scale was carried out by comparison with the experimental iron PDOS derived from the inelastic nuclear scattering experiment. The infrared absorption measurements confirmed the presence of two high-frequency peaks consistent with the calculated PDOS. The calibrated PDOS allowed the calculation of the lattice contribution to the specific heat of KFeS₂ by direct summation over the phonon modes without approximations and adjustable parameters. The temperature-dependent magnetic specific heat evaluated by subtraction of the calculated phonon contribution from the experimental specific heat provides a lower boundary for estimating the reduced spin state of the iron ion.     

Relaxation Processes in Polymer Surface Layers

A recently built and patented device Nanoluminograph is used for the investigation of the relaxation processes in the surface layers of HDPE films, produced at various conditions. The work of the device is based on the phenomenon of radiothermoluminescence. The use of high-frequency low-power, low-temperature plasma as an ionizing source, and a reduction of the consumed energy down to several orders of magnitude (as compared to that used in similar devices) provides excitation of a surface layer as thin as 100–200 nm. The high sensitivity of the device enables one to reduce the excitation time to 1–2 seconds for obtaining a sufficient intensity of glow curves even from ultrathin layers 20–30 nm thick. All of that minimizes the modifying plasma action on the samples under investigation and provides well reproducible and reliable data. It is found that the intensity, number and positions of peaks on the glow curves are strongly influenced by the preparation conditions of polymer films. The complicated profile of glow curve peaks allows one to assume the overlapping of multiple relaxation processes. Decomposing and fitting peak profiles with the help of a PEAKFIT computer program result in revealing at least 4 relaxation transitions in the temperature region from 109 to 213 K. The temperatures and activation energies of relaxation transitions in surface layers appeared to be lower than those inferred from the DSC data for the bulk polymer. The activation energies of trap depletion upon heating are calculated. The nature of traps is discussed in terms of molecular conformations, morphology and structural defects, as well as the attribution of the observed relaxation transitions to defreezing mobility of different kinetic units.     

Sorption and diffusion of low molecular weight gases and vapors in glassy polymers at high concentration of sorbate

A theoretical approach has been developed to describe the sorption and diffusion processes of low weight molecular gases and vapors in polymers at wide ranges of sorbate concentration. The equation of an S‐shaped gas sorption isotherm in glassy polymer matrix has been derived. The concentration dependence of the sorbate molecule diffusion coefficient has been established. For an S‐shaped sorption isotherm, this dependence is nonmonotonous. The conditions of cluster formation of sorbate molecules have been analyzed within the proposed approach, in which it is possible to determine a correlation between these conditions and parameters of sorption isotherm. The comparison of the experimental and theoretical data provides an assessment of the microscopic characteristics of investigated polymer–vapor systems, such as the distances between vapor molecules in a matrix corresponding to intermolecular repulsion and attraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2314–2323, 1999     

Chemical and electrochemical synthesis,structure, photoluminescent properties,and biological activity of 4-methyl-N-[2-[(Z)-2-(2-pyridyl)alkyliminomethyl]phenyl]benzenesulfamide zinc(II) complexes

A series of Zn(II) complexes of the tridentate azomethine ligands, condensation products of 2-(N-tosylamino)benzaldehyde and 2-aminoalkylpyridines, were synthesized by chemical and electrochemical methods. All compounds were characterized on the basis of C, H, N elemental analysis, Fourier-transform infrared, ¹H nuclear magnetic resonance, UV–Vis, and photoluminescence studies. The local atomic structures of complexes were determined from analysis of extended X-ray absorption fine structure and X-ray absorption near-edge structure of Zn K-edges. The molecular structure of chloro-{4-methyl-N-[2-[(Z)-2-pyridyl)ethyliminomethyl]phenyl]benzenesulfamide}zinc(II) was determined by X-ray single-crystal diffraction. The fluorescence spectra show that these complexes in dimethyl sulfoxide solutions at room temperature emit bright blue luminescence at 435–461 nm with fluorescence quantum yields in the range of 0.20–0.31. The assignment and the nature of the bands in experimental UV–Vis spectra of complexes were analyzed using time-dependent density functional theory calculations B3LYP/6-31G(d). The azomethines and complexes of zinc have been screened for their antibacterial, protistocidal, and fungistatic activities against Penicillium italicum, Colpoda steinii, Escherichia coli 078, and Staphylococcus aureus P-209, and the results are compared with the activity of furazolidone, chloroquine, and Fundazol.     

Synthesis and thermodynamic functions of barium cerate co-doped with erbium and indium

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Influence of the Potential-Well Depth on the Reflection of Deuterium Atoms from the Surface of Tungsten

The dependence of the reflection coefficient on the form of the atom—surface interaction potential for the D—W system was found. Potentials with different potential well depths were considered. Calculations were carried out by simulating projectile trajectories and in the binary collision approximation.     

Different Regimes of Ultrashort Pulse Propagation in Disordered Layered Media with Resonant Loss and Gain

Different optical nanostructures containing both loss and gain components attract ever‐increasing attention as novel advanced materials and building blocks for a variety of nanophotonic and plasmonic applications. Unique tunable optical signatures of the so‐called active metamaterials support their utilization for sensing, imaging, and signal processing on micro‐ and nanoscales. However, this tunability requires flexible control over the metamaterial parameters, which could be provided by involving a set of nonlinear interactions. In this paper, a method of governing ultrashort pulses is proposed by varying the level of a population difference disorder in a random active metamaterial. This enables us to deliver three different interaction regimes: self‐induced transparency (low disorder), localization regime (moderate disorder), and light amplification (strong disorder) corresponding to strongly different light pulse speeds. Since this control could be realized via rather plain tools, like simple pump tuning, the proposed disordered medium opens a room of opportunities for designing a peculiar active component for a whole set of highly demanded optical applications.