V. A. Trofimova

X-ray emission spectra of YSr2Cu3O7−δ containing sulphate and phosphate groups

Abstract X-ray emission Kα 1,2 and Kβ 1 spectra of sulphur and phosphorus in [Y 0.89 Sr 0.11 ]Sr 2 Cu 2.78 (SO 4 ) 0.22 O 6.12 and YSr 2 Cu 2.79 (PO 4 ) 0.21 O 6.16 have been investigated. According to an analysis of their fine structure and energy position it is confirmed that the S and P atoms indeed enter superconducting cuprates in the form of oxyanions. It is also found that in YSr 2 Cu 3 O 7−δ containing sulphate groups 0.2 vol.% of CuS is present as an additional phase.

Sulphur-oxygen substitution in YBa2Cu3O6+xSy analyzed by means of X-ray emission spectroscopy

Abstract The analysis of substitution effects upon doping of YBa2Cu3O6+xSy by sulphur is given on the basis of the investigation of S Kα1,2 and S Kβ1 X-ray emission spectra. It is found that sulphur can enter the lattice of YBa2Cu3O7 and substitute oxygen atoms. With increasing sulphur concentration from y > 0.5 to 2.0 S atoms form isolated sulphate groups which do not have a long order but can be detected by X-ray emission spectroscopy.

X-ray spectra and electronic structure of high-Tc superconductors La1.83Sr0.17CuO4 and Bi4Ca3Sr3O16

Abstract X-ray emission, O Kα, Cu Lα, Cu Kβ5 spectra, O 1s total electron yield spectra and Cu K absorption spectra for the high-Tc superconductors La1.83Sr0.17CuO4 and Bi4Ca3Sr3Cu4O16+y have been studied. Spectra of different series and components have been compared in the same energy scale by using Cu 2p and O 1s binding energies and the energies of Cu Kα1 lines. It was found that in given oxides the maximum of O 2p states lies closer to the Fermi level than that of Cu 3d states. Cu 4p states were found to be mixed with the low-energy part of hybridized Cu 3d-O 2p band.

Substitution of SO42− anions in La1.85Sr0.15CuO4: structure and superconductivity

Abstract The possibility of substituting S 2− and SO 4 2− ions into the superconducting cuprate, La 1.85 Sr 0.15 CuO 4 ( T c ≈ 40 K) has been investigated. In contradiction to previous reports, no evidence has been found for the successful incorporation of S 2− into this material, but SO 4 2− groups show limited solubility, and are situated at the copper sites. A change in the cell symmetry from tetragonal to orthorhombic occurs at a substitution level of between 5% and 10%. The presence of sulphur in the form of SO 4 2− groups has been confirmed by X-ray emission spectroscopy for samples prepared from both sulphides and sulphates. Structure refinements based on X-ray powder diffraction data indicate that the SO 4 2− groups are substituting at the copper sites. SQUID measurements have also been performed and show that superconducting properties are adversely affected as the level of substitution is increased.

The X-ray emission spectra and electronic structure of the misfit layer compounds (BiS)1.08NbS2 and (PbS)1.14TaS2

The X-ray emission lines S K beta (3p to 1s) and S L2,3 (3s to 2p) have been measured for the misfit layer compounds (BiS)1.08NbS2 and (PbS)1.14TaS2 and the corresponding binary sulphides Bi2S3, NbS2, PbS and TaS2. The X-ray emission data are compared with X-ray photoelectron spectra and band structure calculations of isolated model layers. The experimental data show very clearly the character of the different valence band states, and partial density of states schemes are easily deduced from these data. A comparison with band structure calculations shows a good agreement with the measured spectra.

X-ray emission spectra and valence state of sulphur atoms of YBa2((CuO)1-x(NiS)x)3O4- delta

SK alpha 1,2 and SK beta 1 fluorescence X-ray emission spectra of YBa2(CuO1-x(NiS)x)3O4- delta (x=0.01; 0.03) are investigated. According to analysis of their energy position and fine structure one can conclude that sulphur atoms enter the lattice of Y123 compounds and form oxyanion groups. The oxidation state of S atoms in these compounds depends on their concentration and varies from 4+ to 6+.

VALENCE BAND SPECTRA OF BaCo1−xNixS2

Abstract The band properties of the quasi two-dimensional transition metal sulphide alloy system BaCo 1 − x Ni x S 2 ( x =0, 0.1, 0.2, 0.5, 1.0) have been studied by X-ray photoelectron, X-ray absorption and X-ray fluorescence spectroscopy with tunable synchrotron radiation. It is found that the metallic character of the BaCo 1 − x Ni x S 2 system increases with x in accordance with the results of transport property measurements. The S L 2,3 X-ray emission spectra show an excitation energy dependence which allowed separate mapping of the distribution of S(2) and S(1)+S(2) 3s3d partial density of states.

Possibility of sulphur-oxygen substitution in YBa2Cu3O6+xSy analyzed by means of X-ray emission spectroscopy

Abstract The analysis of substitution effects upon doping of YBa 2 Cu 3 O 6+x S y by sulphur is given on the basis of investigation of SKα 1,2 and SKs 1 x-ray emission spectra. It is found that sulphur can enter the lattice of YBa 2 Cu 3 O 7 and substitute oxygen atoms. With increasing sulphur concentration from y>0.5 to 2.0 S atoms form isolated sulphate groups which do not have a long order but can be detected by x-ray emission spectroscopy.

Electronic structure of ternary transition metal oxides and sulphides: X-ray photoelectron and X-ray emission spectroscopy study

Abstract Results of measurements of X-ray photoelectron spectra (XPS) and X-ray emission spectra (XES) of constituents atoms (excited by electrons and tunable synchrotron radiation) of ternary transition metal oxides (EuMnO 3 , Sr 2 RuO 4 ) and sulphides (BaCo 1−x Ni x S 2 are presented. They are compared with LDA and LDA + U band structure calculations. For Sr 2 RuO 4 and BaCo 1− x Ni x S 2 energy excitation dependence of O Kα and S L 2,3 XES near the O 1s and S 2p threshold is found which is attributed to excitation of inequivalent oxygen and sulphur atoms in plane and apical sites, and corresponding O 2p and S 3s3d DOS are mapped.

Electronic structure of advanced materials studied by x-ray emission spectroscopy

High resolution soft x-ray emission spectroscopy with high spatial resolution is used to study of the electronic structure and characterize advanced materials: high-Tc superconductors, transition metal compounds, porous silicon, solid-solid buried interfaces and hard materials. In high-Tc, the main attention is focused on the analysis of oxygen-cation interactions and the determination of the location of impurity atoms. In transition metal compounds the participation of different electronic states of constitute atoms in the valence band is analyzed and correctness of LDA band structure calculations is estimated. For CuFeO2 an unusual mutual position of the Cu3d and Fe3d bands was found which is attributed to strong electron-electron correlations. In porous silicon the local structure of silicon atoms is found to depend on the type of doping of the initial Si wafer. Solid-solid buried interfaces in thin semiconducting films irradiated by eximer laser are investigated. For the hard materials boron-carbonitr...