Core hole satellites in NixPd1-x alloys

The two and three hole satellites accompanying the main Ni 2p and Pd 3d XPS core lines in Ni_xPd_1-x alloys have been measured as function of the alloy concentration. The changes in satellite distance with concentration cannot be explained by the thermochemical approach, which has recently been shown to describe successfully the one hole core level binding energy shifts (main line) in alloys. The reason is probably, that in this approach, which uses thermochemical data of Z + 1, Z + 2 and Z + 3 elements - where Z stands for Ni or Pd and Z + n is the nth element following them in the periodic table - d-band contributions to the cohesive energies of the final d-hole states are neglected.     

Mössbauer studies in disordered (NiFe)1−xCrx alloys

The variation of hyperfine field, isomer shift and Curie temperature with chromium concentration has been studied for the alloys (NiFe)_1?xCr_x for x = 0, 5, 10 and 15 at .%. The decrease in hyperfine field and isomer shift suggests an emptying of the majority spin d-band with increasing Cr concentration (reducing number of average 3d + 4s electrons per atom). The Curie temperature is also found to reduce rapidly with Cr concentration in agreement with magnetisation data. But the Curie temperatures as determined from Mössbauer spectra are considerably lower than those given by magnetisation studies and for the 10 and 15 at .% Cr concentrations the magnetic transition is spread out over a range of temperatures suggesting a mictomagnetic behaviour.     

Magnetic field induced order–order phase transition in magnetocaloric systems Mn2−xFexAs0.5P0.5 and MnFeAsyP1−y

An analysis is presented of experimental and theoretical results of the MnFeAs_yP_1−y (0.15≤y≤0.66) and Mn_2−xFe_xAs_0.5P_0.5 (0.5≤x≤1.0) systems to identify main traits that underlie the mechanism of formation of different antiferromagnetic (AF) phases in the two systems. The discrepancy between the calculated from first principles and experimental values of the magnetic moment in the ferromagnetic phase with cation substitution in the system Mn_2−xFe_xAs_0.5P_0.5 is due to the appearance of a canted magnetic structure. In this case, the emergence of an AF phase with decreasing iron concentration precedes a significant change in the electronic d-band filling. In the model of the spiral structure in the system of itinerant electrons it is shown that the stabilization of the AF phase with decreasing arsenic concentration, while maintaining the number of d-electrons, is a consequence of changes in the shape of the density of electronic states that occur with a decrease in unit-cell volume.     

Two independent magnetic sublattices of Er in the Er5 − x LaxGe3 system

Magnetic measurements of Er_{5 ? x} La_xGe₃ with 1 ? x ? 5 have been done between 4·2 and room temperature. The compounds crystallize in the hexagonal (D8₈) structure (Mn₅Si₃ type) with space group P6₃/mcm. Two independent, ferromagnetic and antiferromagnetic, sublattices of Er exist. The magnetic interaction between the Er atoms in the 6(g) sites is ferromagnetic, while that between the Er atoms in the 4(d) sites is antiferromagnetic. The antiferromagnetic exchange interaction is weak in this system. The first and second La atom substitutes into the 6(g) site, while the third La in Er₂La₃Ge₃ is located in the 4(d) position. The fourth La is probably substituted in such a manner that all the Er atoms are left in the 6(g) sites.     

Effect of Cu deficiency on the optical properties and electronic structure of CuIn1−xGaxSe2

Spectroscopic ellipsometry measurements of CuInSe₂ (CIS) and CuIn_1−xGa_xSe₂ (CIGS) over a range of Cu compositions reveal that there are important differences in electronic and optical properties between α-phase CIS/CIGS and Cu-poor CIS/CIGS. We find a reduction in the imaginary part of the dielectric function ?₂ in the spectral region, 1-3 eV. This reduction can be explained in terms of the Cu-3d density of states. An increase in band gap is found for Cu-poor CIS and CIGS due to the reduction in repulsive interaction between Cu-3d and Se-4p states. We also characterize the dielectric functions of polycrystalline thin-film α-phase CuIn_1−xGa_xSe₂ (x=0.18 and 0.36) to determine their optical properties and compare them with similar compositions of bulk polycrystalline CuIn_1−xGa_xSe₂. The experimental results have important implications for understanding the functioning of polycrystalline optoelectronic devices.     

Ab initio study of 5d-shells Ir substitution for Fe-based SmOFe1−xIrxAs

The lattice and electronic properties for 5d-shells Ir substituted Fe-based superconductor SmOFe_1−xIr_xAs (x=0,0.2,0.25,0.3) are investigated based on the density functional theory (DFT) with a spin generalized gradient approximation SGGA+U method. The electronic density of states (DOS) of SmOFe_1−xIr_xAs is studied and well compared with the results of experimental X-ray photoemission spectroscopy (XPS). The calculation indicated that iridium substitution at the Fe site induced a modification of the FeAs₄ tetrahedron and suppressed the magnetic ordering corresponding to the Fe-3d, which may be the main cause of inducing superconductivity in Ir-doped SmOFeAs system.     

Valence band states of semi-magnetic semiconductors: Cd1-xMnxTe

Valence band electron states of Cd_1-xMn_xTe mixed crystals were determined over the composition range 0?x?0.7 by ultra-violet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). A peak at 3.5 eV binding energy (BE) whose magnitude increases with the manganese mole fraction x was identified as originating from the Mn 3d⁵ level. A previously reported structure at 6.5 eV BE was also observed for x>0.4; it is, however, believed to be a satellite of the 3.5 eV peak originating from a shake-up process.     

Spontaneous volume magnetostriction in Y(Fe1−xCox)2 and Zr(Fe1−xCox)2

The spontaneous volume magnetostriction is calculated for Y(Fe_1?xCo_x)₂ and Zr(Fe_1?xCo_x)₂ in the simple itinerant-electron model. The density of states for various compositions is calculated by the recursion method. The calculated results on the composition dependence of the spontaneous volume magnetostriction are shown to be consistent with the experimental ones.     

Luminescence properties of LiPrxCe1−xP4O12

LiPr_1−xCe_xP₄O₁₂ (x=0, 0.002, 0.02; 0.1) powder samples were prepared using the melt solution technique. Luminescent parameters of LiPr_1−xCe_xP₄O₁₂ phosphors have been investigated under ultraviolet-vacuum ultraviolet (3-12 eV) synchrotron radiation and X-rays excitation at room and near liquid He temperatures. Excitation luminescence spectra of Ce³⁺ emission, luminescent spectra and decay curves from the lower excited state levels of the 4f¹5d¹ and 5d¹ electronic configuration of the Pr³⁺ and Ce³⁺, respectively, clearly indicate energy transfer from Pr³⁺ to Ce³⁺. Energy migration proceeds via the Pr-sublattice followed by nonradiation transfer from Pr³⁺ to Ce³⁺ ions.     

X-ray investigation of the mean square thermal displacements in VDx, NbHx and TaHx interstitial alloys

X-Ray measurements of the integrated Bragg intensities from V, Nb and Ta single crystals as a function of hydrogen (D) concentration and temperature have been carried out. Two different methods were applied: (i) the usual angular dispersive method using MoK_α1 characteristic radiation; and (ii) the energy dispersive method using the white spectrum of the Mo tube and an intrinsic Ge detector. From the results the thermal Debye-Waller factor for the three metals and its change with hydrogen concentration are determined. The mean square of the thermal displacements (u²) decreases with hydrogen (D) concentration. For NbH_x(D_x) this agrees well with (u²) values as determined from measured phonon density of states spectra. The results are also given in terms of a Debye temperature depending on H(D) concentration.     

Alloying effects on the optical absorption edge of glow-discharge a-Si1-xGex: H

The absorption edge of glow-discharge a-Si_1-xGe_x: H alloys with Ge concentrations varying from 0 to 38% is determined from optical and photoconductivity measurements. The alloying effects on the band edges and the density of localized states in the pseudo-gap are discussed in relation with modifications of the photoconduction response.     

Direct observation of occupied gap states in amorphous Si1-xGex: H alloys by SXS

SiKβ emission band have been analysed from a-Si_1-xGe_x: H alloys for Ge concentrations varying from 0.05 to 0.60. Localized states with p character are observed in the pseudo-gap near the valence band edge.     

Study of the [(Co45Fe45Zr10)x(Al2O3)100−x/a-Si:H]m multilayer nanostructure by polarized neutron reflectometry

Polarized neutron reflectometry was used to investigate the amorphous multilayer nanostructures [(Co₄₅Fe₄₅Zr₁₀)_x(Al₂O₃)_100−x/a-Si:H]_m, whose magnetic properties are dependent on the concentration of the magnetic constituent (x=34, 47 and 60 at%) as well as on the thicknesses of the metal-dielectric (Co₄₅Fe₄₅Zr₁₀)_x(Al₂O₃)_100−x and semiconductor a-Si:H layers. The average magnetization of the individual magnetic layer is found to be inhomogeneous with the magnetically active central part and two magnetically dead parts at the interfaces.     

The suppression of structural phase transformation in LaVO3 and La1−xSrxVO3 thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of LaVO₃ and La_1−xSr_xVO₃ have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175<x<0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of LaVO₃ and La_1−xSr_xVO₃ fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear (T^1.5) behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of V³⁺ and V⁴⁺ ions as the value of x increases.     

The electronic structure and properties of Fe6(N1−xCx)2 carbonitrides by first-principles calculations

Electronic structure and properties of Fe₆(N_1−xC_x)₂ carbonitrides with 0≤x≤1, i.e. the concentrations of N and C elements are respectively in range of 0∼7.69 wt% and 0∼6.67 wt%, have been studied by first-principles calculations based on density functional theory (DFT) implemented in the Cambridge Serial Total Energy Package (CASTEP) code. The calculated results show that the Fe₆(N_1−xC_x)₂ carbonitrides are thermodynamically and mechanically stable. Lattice parameters and stability of the carbonitrides increase when C atoms replace N atoms in Fe₆N₂ unit cell. In Fe₆(N_1−xC_x)₂ unit cell, the hybridization effect between C-2p and Fe-3d states is stronger than that between N-2p and Fe-3d states. Elastic properties and melting points of the carbonitrides change slightly with the substitution of C atoms for N atoms in Fe₆(N_1−xC_x)₂ carbonitrides.     

Luminescence study of LiGa5−xFexO8

Absorption, excitation, and luminescence measurements are presented for LiGa_5?xFe_xO₈ with concentrations x from 0.015 to 0.26. The emission and excitation data indicate that the red luminescence observed is due to the ⁶A₁(⁶S)←⁴T₁(⁴G) transition in the d⁵ configuration for Fe³⁺ in tetrahedral sites. Single-crystal samples allow direct absorption measurements for the first time and these indicate that most of the Fe³⁺ substitutes for Ga³⁺ in octahedral sites. Fine structure in the zero-phonon line and in the sideband is reported.     

First-principles calculations on the role of Ni-doping in Cun clusters: From geometric and electronic structures to chemical activities towards CO2

First-principles calculations have been applied to investigate the role of Ni-doping in modifying the geometric and electronic structures of Cu_n clusters (n=1-12), and the chemical activity of clusters towards CO₂. The results reveal that Ni-doping introduces a significant modulation of the electronic structures, such as the density of states, HOMO-LUMO gaps and the d-band centers, which dominate their chemical activities towards CO₂ adsorption. Our findings contribute valuable information for high efficient Cu-Ni alloy nano-catalyst design.     

Structural study of Pr1−xCaxMnO3 and Y1−xCaxMnO3 perovskites

The structural properties of Prx_1?xCa_xMnO₃ and Y_1?xCa_xMnO₃ perovskite systems were studied by X-ray and magnetic susceptibility measurements. The differences in the structural properties of both systems are attributed to the differences of tolerance factors, i.e. of ionic radii of the ions present and the results are interpreted as being due to simultaneous action of steric effect, orbit-lattice interactions of Mn³⁺ ions and Coulomb interactions among 3d electrons. Their individual contributions depending on the compositions are analyzed. Besides the usual cooperative Jahn-Teller effect existing in PrMnO₃ a new type of transformation was found which is connected, under condition of Mn³⁺ ? Mn⁴⁺ valency migration, with the formation of local Jahn-Teller distortions. It is characterized by the equality of v_hop and v_phon at a critical temperature T_crit; it has been found that T_crit depends only very weakly on the composition. A correpsonding O'→O change in the yttrium system is, however, rather continuous which is explained by a strong influence of the cooperative buckling effect. An analysis of the magnetic data points to the presence of double exchange in the praseodymium system at high temperatures, while at low temperatures this mechanism applies only in the region, where cooperative Jahn-Teller effect exists, i.e. at x0.4.     

Growth, optical properties and laser performance of NdxLu1−xVO4 series crystals

Nd_xLu_1−xVO₄ (x = 0, 0.005, 0.02, 0.023, 0.03 and 0.05) series crystals have been grown by the Czochralski method. The results of X-ray powder diffraction experiments show that these crystals belong to the zircon-type structure. The cutoff wavelength of LuVO₄ is 330 nm and the transmittance is about 80% in 540-3010 nm. The functional relation of absorption coefficient α at 808 nm on Nd³⁺-doped concentration N_d in units of atomic % is obtained to be α = 7.649 N_d. The results of Judd-Ofelt analysis show that there is no obvious concentration quenching effect below 3 at.% doped concentrations. The highest output power at 1.06 μm is 1090 mW for Nd_0.02Lu_0.98VO₄ at the pumping power of 6.58 W of a laser diode, the optical-optical conversion efficiency is 16.6% and slope efficiency is 19.4%.     

X-ray spectroscopic study of the valence band structure of Cd1−xMnxTe, x = 0.6

The valence band structure of Cd_1?xMn_xTe (x = 0.6) was studied by soft X-ray emission spectroscopy using a 11.5 m concave grating grazing incidence spectrometer in conjunction with a high power rotating anode, which provided the radiation for flourescence excitation. The position of the Mn 3d⁵ states within the energy band system could be identified unambiguously; they form a band near the top of the CdTe valence band. The results are discussed with regard to recently published photoemission data.