Site Occupation Preferences in CdMnTeSe Quaternary Alloys. EXAFS Data Analysis

Site occupation preferences in zinc-blende Cd1-xMnxTe1-ySey (0≤x≤0.15; 0.0≤y≤0.20) quaternary alloys have been determined by the Extended X-ray Absorption Fine Structure (EXAFS) analysis. The experimental data have been collected with the use of synchrotron radiation for Se- and Mn-K edges. For both K edges, the preferences of manganese distribution around selenium have been observed and analyzed. The Mn-Se with Cd-Se, and Mn-Se with Mn-Te distances have been found as linearly dependent on concentration of Se and Mn. The average coordination numbers of Mn around Se versus Mn composition was approximated by the quadratic behavior instead of the linear dependence expected for the virtual crystal approximation, in which a full random distribution of elements in the sublattices is assumed. The obtained results support the preferential occurring of Mn and Se ions in the considered compounds. A structural and magnetic interaction reasons of the preferences were discussed

Vibrational and crystalline properties of polymorphic CuInC2 (C=Se,S) chalcogenides

This paper deals with the analysis of the vibrational and crystallographic properties of CuInC2 sC=S,Sed chalcogenides. Experimentally, evidence on the coexistence in epitaxial layers of domains with different crystalline order—corresponding to the equilibrium chalcopyrite sCHd and to CuAu sCAd—has been obtained by cross section transmission electron microsopy sTEMd and high resolution TEM sHREMd. Electron diffraction and HREM images give the crystalline relationship f110gCHif100gCA and s112dCHis011dCA, observing the existence of a s112dCHis001dCA interphase between different ordered domains. The vibrational properties of these polytypes have been investigated by Raman scattering. Raman scattering, in conjunction with XRD, has allowed identifying the presence of additional bands in the Raman spectra with vibrational modes of the CA ordered phase. In order to interpret these spectra, a valence field force model has been developed to calculate the zone-center vibrational modes of the CA structure for both CuInS2 and CuInSe2 compounds. The results of this calculation have led to the identification, in both cases, of the main additional band in the spectra with the total symmetric mode from the CuAu lattice. This identification is also supported by first-principles frozenphonon calculations. Finally, the defect structure at the interphase boundaries between different polymorphic domains has also been investigated

Dynamical properties of ordered Fe-Pt alloys

© 2015 Elsevier B.V. All rights reserved. The structure, magnetic properties, and lattice dynamics of ordered Fe-Pt alloys with three stoichiometric compositions, Fe3Pt, FePt and FePt3, have been investigated using the density functional theory. Additionally, the existing experimental data have been complemented by new measurements of the Fe projected phonon density of states performed for the Fe3Pt and FePt3 thin films using the nuclear inelastic scattering technique. The calculated phonon dispersion relations and phonon density of states have been compared with the experimental data. The dispersion curves are very well reproduced by the calculations, although, the softening of the transversal acoustic mode TA1 leads to some discrepancy between the theory and experiment in Fe3Pt. A very good agreement between the measured spectra and calculations performed for the tetragonal structure derived from the soft mode may signal that the tetragonal phase with the space group P4/mbm plays an important role in the martensitic transformation observed in Fe3Pt. For FePt3, the antiferromagnetic order appearing with decreasing temperature has been also investigated. The studies showed that the phonon density of states of FePt3 very weakly depends on the magnetic configuration.publisher: Elsevier articletitle: Dynamical properties of ordered Fe–Pt alloys journaltitle: Journal of Alloys and Compounds articlelink: http://dx.doi.org/10.1016/j.jallcom.2015.08.097 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved.status: publishe

Statistical model analysis of local structure of quaternary sphalerite crystals

At the 2004 Ural International Winter School, we introduced the statistical strained tetrahedron model and discussed ternary tetrahedron structured crystals. The model allows one to interpret x-ray absorption fine structure (EXAFS) data and extract quantitative information on ion site occupation preferences and on the size and shape of each elemental constituent of the configuration tetrahedra. Here we extend the model to cover quaternary sphalerite crystal structures. We discuss the two topologically different quaternary sphalerite systems: the pseudo balanced A₁₋xBxYyZ₁₋y (2:2 cation:anion ratio), and the unbalanced AxBx C₁₋x₋x Z or AXyYy Z₁₋y₋y (3:1 or 1:3 cation:anion ratios) truly quaternary alloy systems. These structural differences cause preference values in pseudo quaternaries to vary with the relative contents, but to remain constant in truly quaternary compounds. We give equations to determine preference coefficient values from EXAFS or phonon spectra and to extract nearest-neighbour inter-ion distances by EXAFS spectroscopy. The procedure is illustrated and tested on CdMnSeTe, GaInAsSb, and ZnCdHgTe quaternary alloys

Thermal expansion and elasticity of PdFe 3N within the quasiharmonic approximation

We have explored the bulk modulus and the thermal expansion of PdFe 3N (space group $Pm\overline 3 m$ ) using ab initio phonon dynamics within the quasiharmonic approximation in the temperature range from 50 to 1000 K. PdFe 3N possesses a linear thermal expansion coefficient common for typical ceramics. The calculated average linear thermal expansion coefficient of 6.4 × 10 -6 K -1 is consistent with the average measured coefficient of 6.7 × 10 -6 K -1 . We have shown here that the thermal behavior of this compound can be understood based on the electronic structure and the lattice dynamics thereof. PdFe 3N exhibits both metallic as well as covalent-ionic bonding. The Fe–N covalent-ionic bonding suppresses the lattice vibrations of the PdFe 3 matrix. The bulk modulus of 188 GPa for PdFe 3N decreases by 15% in the temperature range studied, which is expected due to presence of stiff Fe–N bonds. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010