Magnetic phase diagram and transport properties of FeGe_2

We have used resistivity measurements to study the magnetic phase diagram of the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K in magnetic fields up to 16 T. In contrast to theoretical predictions, the incommensurate spin density wave phase is found to be stable at least up to 16 T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied the low temperature magnetoresistance in the [100], [110], and [001] directions. The transverse magnetoresistance is well described by a power law for magnetic fields above 1 T with no saturation observed at high fields. We discuss our results in terms of the magnetic structure and the calculated electronic bandstructure of FeGe_2. We have also observed, for the first time in this compound, Shubnikov-de Haas oscillations in the transverse magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along [001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of Physics: Condensed Matte

Characterization of TiAlSiON coatings deposited by plasma enhanced magnetron sputtering: XRD, XPS, and DFT studies

The results of characterization of TiAlSiON hard coatings deposited on ferric-chromium AISI 430 stainless steel by plasma enhanced magnetron sputtering are presented. The coating with maximum hardness (of 43GPa) was obtained at the following optimal values of elemental concentrations: Si ~5at.%, Al ~15at.%, and Ti ~27at.%. The value of gaseous mixture (Ar-N2) pressure was of 0.13Pa and the value of partial pressure of oxygen (O2) was 1.3·10-3Pa. The X-ray diffraction (XRD) measurements showed the presence of Ti(Al)N. High-energy resolved XPS spectra of core levels revealed the formation of Ti-N, Ti-O-N, Si-N and Al-O-N bonds. Comparison of XPS valence band spectra with specially performed density functional theory calculations for disordered Ti0.5Al0.5N1-xOx (0≤x≤0.3) phases demonstrated that a Ti(Al)OxNy phase is formed on the surface of AISI430 steel upon the plasma enhanced magnetron sputtering, which can provide a good combination of high hardness and additional oxidation resistance of this material. © 2015 Elsevier B.V

Electronic structure and properties of strontium ferrite Sr 3Fe 2O 6

The electronic structure of strontium ferrite Sr 3Fe 2O 6 was calculated using the tight-binding linear muffin-tin orbital method (TB LMTO) in the local spin density approximation of density functional theory with Coulomb correlations correction (LSDA+U). The semiconducting character of the spectrum with charge transfer energy gap of 1.82 eV was obtained in reasonably good agreement with experimental data. The iron ions are found to be in the high spin state. The calculated value of the local spin magnetic moment of Fe 3+ ion is 3.94 μ B which is not typical for trivalent iron ion in the high spin state. It is shown that the strong hybridization between Fe3d and O2p orbitals favors the d 6 L configuration of Fe 3+ ion, where L is a hole in the oxygen p shell. The mechanism of oxygen transport in ferrite is discussed basing on the total energy calculations of the different spatial configurations of oxygen vacancies. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200671.20.-b Electron density of states and band structure of crystalline solids, 71.27.+a Strongly correlated electron systems; heavy fermions, 72.10.-d Theory of electronic transport; scattering mechanisms, 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) ,

Ab initio approach to structural, electronic and optical properties of B-, C- and N-doped anatase

18 páginas.The effect of doping with boron, carbon and nitrogen on crystal lattice parameters, electronic band structure and optical absorption of anatase has been studied by means of an ab initio density functional theory approach. The investigations included optimization of crystal structure based on the pseudo-potential plane-wave approach. The spin-polarized calculations of the band structure with the account of on-site Coulomb correlations (LSDA+U) employing the tight-binding linear muffin-tin orbitals method (TB-LMTO) have also been performed. The evaluations of optical absorption were based on the calculations of dielectric function with local field effects taken into account. We find that the crystal lattice relaxation around the doping atoms produces noticeable changes in the band structure, magnetic state and optical properties of the doped compounds. The most considerable effects are the collapse of magnetic moment on carbon atom and an essential reduction of the optical absorption in the region of the impurity band — impurity band transitions. Comparing optical absorption for different kinds of doping and taking into account the intensity distribution of the solar light we come to the conclusion than the doping with boron is the most promising kind of doping for photocatalytic applications of the doped anatase.Peer reviewe

Сlinical results of transepithelial corneal collagen crosslinking in patients with keratoconus

Purpose: To evaluate the clinical results of transepithelial corneal collagen crosslinking (CXL) compared with the standard CXL in patients with keratoconus.Patients and methods. There were 94 patients (119 eyes) with I‑III stage keratoconus (according to the Amsler classification) under observation since 2011 to 2013. The first group included 43 patients(56 eyes) among them 11 patients (11 eyes) with an initially thin cornea (380‑430 microns) underwent transepithelial CXL. 51 patients (63 eyes) in the second group — the standard CXL. Saturation of the cornea with a photosensitizer during transepithelial CXL was performed via electrophoresis using the «Potok-1» device, in the amperage of 1 mA for 10 minutes. CXL was performed with the use of «UFalink» device and «Dextralink» photosensitizer.Results. Pseudo haze of corneal stroma was diagnosed on biomicroscopy after both methods of CXL. In the 1st group in 38 % of cases (30 eyes) it disappeared in 2‑4 weeks after the CXL, in the 2nd group in 100 % of cases (63 eyes) it resolved in 3‑4 months, on average, after the treatment. According to optical coherence tomography (OCT) in two weeks after transepithelial CXL there was a demarcation line in 27 eyes (48.2 %) after 1 month — in 15 (26.7 %), at a later stage — has not been determined. After a standard CXL demarcation line was determined during the first two weeks in all patients (100 %) and persisted until 12 months in 2 eyes (3.5 %). Indicator of cornea’s refractive power in 2 years after transepithelial CXL decreased by 1.5 D (p> 0.05) compared to baseline values after standard CXL decreased by 1.8 D (p>0.05). Uncorrected visual acuity after transepithelial CXL increased from 0,31±0,01 to 0,45± 0,05 (p<0.05) in 2 years, after the standard CXL — from 0,27±0,03 to 0.3±0,05 (r≥0,05). Corrected visual acuity (CVA) in both groups tended to increase over the two-year followup. The obtained comparable results showed that the use of transepithelial and standard methods of CXL in patients with keratoconus prevents disease progression in 73.2 % and 77.7 % respectively what confirms the possibility of its equal usage in clinical practice.Conclusion. Transepithelial CXL with photosensitizer saturation by electrophoresis does not require de-epithelization, it’s well-tolerated and does not cause pain. This technique is equa the standard CXL procedure. It improves optometric data and stabilizes the disease process

ELECTRONIC STRUCTURE OF Sr-DOPED LaScO3 UNDER H2 AND H2O UPTAKE

This work presents joint results on the optical properties and modeling of energy levels in the vicinity of the band-gap for Sr-doped lanthanum scandate.This work was financially supported by RSF (Project No. 16-13-00053) and Minobrnauki of Russia (assignments No. АААА-А18-118020190098-5, No. AAAA-A18-118111290051-4)

Electronic structure of nonstoichiometric compounds in the coherent potential approximation

We formulate and implement a method for electronic structure calculations based on the coherent potential approximation. This method provides an accurate description for nonstoichiometric compounds with the disordered location of vacancies. In the essence of its formulation, the method is similar to the implementation of the local electron density approximation in combination with the dynamical mean field theory (LDA + DMFT) and, hence, it can be easily incorporated in the latter approach. We study the evolution of the electronic structure of titanium dioxide TiO 2 - δ (rutile) with the growth of nonstoichiometry in the oxygen sublattice. The results of the calculations are compared to the experimental data on the photoemission spectra. © 2011 Pleiades Publishing, Ltd

Microarc Oxidation of the High-Silicon Aluminum AK12D Alloy

The aim of work is to study how the high-silicon aluminum AK12D alloy microstructure and MAO-process modes influence on characteristics (microhardness, porosity and thickness of the oxide layer) of formed surface layer.Experimental methods of study:1) MAO processing of AK12D alloy disc-shaped samples. MAO modes features are concentration of electrolyte components – soluble water glass Na2SiO3 and potassium hydroxide (KOH). The content of two components both the soluble water glass and the potassium hydroxide was changed at once, with their concentration ratio remaining constant;2) metallographic analysis of AK12D alloy structure using an optical microscope «Olympus GX51»;3) image analysis of the system "alloy AK12D - MAO - layer" using a scanning electron microscope «JEOL JSM 6490LV»;4) hardness evaluation of the MAO-layers using a micro-hardness tester «Struers Duramin».The porosity, microhardness and thickness of MAO-layer formed on samples with different initial structures are analyzed in detail. Attention is paid to the influence of MAO process modes on the quality layer.It has been proved that the MAO processing allows reaching quality coverage with high microhardness values of 1200-1300HV and thickness up to 114 μm on high-silicon aluminum alloy. It has been found that the initial microstructure of alloy greatly affects the thickness of the MAO - layer. The paper explains the observed effect using the physical principles of MAO process and the nature of silicon particles distribution in the billet volume.It has been shown that increasing concentration of sodium silicate and potassium hydroxide in the electrolyte results in thicker coating and high microhardness.It has been revealed that high microhardness is observed in the thicker MAO-layers.Conclusions:1) The microstructure of aluminum AK12D alloy and concentration of electrolyte components - liquid glass Na2SiO3 and potassium hydroxide affect the quality of coating resulted from MAO-processing.2) Increasing concentration of the electrolyte leads to the thicker MAO-layer of higher microhardness and lower porosity.3) Deformation-heat treatment of AK12D alloy samples using a scheme "forging + quenching + aging" before the MAO leads to deteriorated quality of formed layer.</p