This report was prepared as an account of work sponsored by an agency of the United States Govern... more This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. By acceptance of thisarticle,the publisher recognized that theU S Government retainsa nonexclusive, royalty-free licensetopublishor reproduce thepublished formof thiso._n_ibution or to allowotherstodo soforU S Government purposes. TheLosAlamos National Laboratory requests thatthe publisher identifythisarticle asworkperformed underthe auspices of theU S Department of Energy.
Coexisting electronic correlations and electron-phonon interactions have been proposed to lead to... more Coexisting electronic correlations and electron-phonon interactions have been proposed to lead to dynamic polaron-tunneling behavior for the axial oxygen in YBa2Cu307. Emphasizing nonlinear and nonadiabatic effects, we show that this description leads to distinctive predictions consistent with structural, optical, and inelastic neutron-scattering data in the axial direction.
ABSTRACT Polarized Cu—K edge XAFS (X-ray absorption fine structure) on La2CuO4.1 indicate that th... more ABSTRACT Polarized Cu—K edge XAFS (X-ray absorption fine structure) on La2CuO4.1 indicate that the radial distribution function of the copper in plane oxygen pairs is a two-site distribution, in agreement with the results found by Bianconi et al. for temperatures below the appearance of a pseudogap. Additionally we find evidence of a change in this distribution across the superconducting transition, suggesting coupling between the local lattice structure and the charged particles involved in the superconductivity.
We performed near edge x-ray absorption spectroscopy (XANES) measurements on the Arsenic K-edge o... more We performed near edge x-ray absorption spectroscopy (XANES) measurements on the Arsenic K-edge of As(III) in solution under acidic and basic conditions, after exposure of the solutions to air. Spectra were recorded for increasing exposure times to the x-rays used to perform absorption spectroscopy measurements. We did not find changes for the solution under acidic conditions, while we observed significant changes in the case of solution under alkaline conditions. In order to interpret these changes, we compared the obtained spectra with XANES spectra of As(III) and As(V) solutions under alkaline conditions, not exposed to air, and used as standards. Principal component fits using these standards indicate an accelerated conversion of As(III) to As(V) due to the exposure to x-rays.
The effect of isotopic substitution in the excitation spectrum of a model polaronic system is pre... more The effect of isotopic substitution in the excitation spectrum of a model polaronic system is presented. To study this effect we use a three-site many-body Hamiltonian, with two phonon modes, which includes electronic correlations and electron-phonon interactions. Under isotopic substitution, the shift of the lowest excitation energy changes sign for intermediate electron-phonon coupling, coinciding with the onset of polaronic behavior. This manifests as a strong change of the dynamics of polaron tunneling, a behavior opposite to that found in purely phonon excitations. Additionally, a small change in the static polaronic distortion appears under isotopic substitution. This change in the local structure has opposite signs for low and intermediate electron-phonon coupling compared to that found in the strong-coupling limit. ͓S0163-1829͑99͒08013-3͔ PHYSICAL REVIEW B
X-ray pair distribution function (pdf) and U L 3 extended x-ray absorption fine structure (EXAFS)... more X-ray pair distribution function (pdf) and U L 3 extended x-ray absorption fine structure (EXAFS) and neutron pdf measurements that give identical results for UO 2 show U(VI)-oxo moieties with x rays for mixed valence U 4 O 9 and U 3 O 7 , in contrast to the neutron data that indicate only U(V) sites with no short U-O bonds as well as other differences. In addition, although the EXAFS spectra of UO 2 are essentially identical at 30, 100, and 200 K, those of the UO 2+x compounds exhibit different nearest-neighbor U-O distributions at each temperature. Further tunneling polaron-type behavior is found in the broadening of the features of the O K-edge x-ray absorption spectra (XAS) of the UO 2+x compounds. Raman spectra of powders also show a large increase in scattering cross section with increasing O content that would originate in a change in the electronic structure that increases the overall polarizability. The XAS and Raman also show that U 4 O 9 does not behave as a linear combination of the UO 2 and U 3 O 7 fluorite endpoints. The properties induced by mobile rather than static charged quasiparticles were explored by optical pumping of the metal-to-metal charge-transfer transition. The temperature dependence of 4.71 eV pump-1.57 eV probe reflectivity on UO 2 that initially populates the U 6d-dominated portion of the upper Hubbard band (UHB) shows a sharp 28-μsec lifetime peak at 25 K that may be associated with the fluctuations of its antiferromagnetic transition. Pumping at 3.14 eV into the 5f-dominated portion of the UHB shows an analogous 2.8-μsec peak but also a plateau bracketing this peak that ends in a cusp at 50-60 K and an abrupt change in the hardening rate of a novel 12-15 GHz phonon that is the signature for the quasiparticle quantum phase. The different results for the different excitation channels indicate a highly specific nonthermal relaxation mechanism. These results constitute the first observation of a distinct phase of photoinduced quasiparticles that is sufficiently coupled to the lattice to undergo a gap-opening transition. When the intragap state is probed with a terahertz time domain spectroscopy (TTDS) measurement 33 psec after a 3.14 excitation pulse, it shows increased absorption in the 0.5-1.1 THz range with a decrease in temperature from ∼30 to 10 K instead of the expected decrease, a result consistent with the presence of a condensate. These results are too extreme to originate in the dynamical, nonadiabatic, coupled charge-transfer-phonon/tunneling polaron scenario previously used for doped Mott-Hubbard insulators with intermediate electron-phonon coupling and therefore indicate novel physics. One possibility that could cause all of these behaviors is that a collective, dynamical, charge transfer-coupled Peierls distortion involving the 2 U(V) ↔ U(IV) + U(VI)-oxo excitation occurs coherently over an entire domain to cause the atoms in this domain to condense into a system with Bose-Einstein or Bose-Einstein-Hubbard properties.
Journal of Superconductivity and Novel Magnetism, 2013
ABSTRACT Ab initio Fe K-edge X-ray absorption near edge structure (XANES) calculations on FeTe1−x... more ABSTRACT Ab initio Fe K-edge X-ray absorption near edge structure (XANES) calculations on FeTe1−x Sex , based on its crystallographic structure, are compared with experimental data. The calculated XANES spectra are inconsistent with the observed increase of spectral weight in the preedge region of the experimental spectra on the ternary system in which Te is substituted by Se. However, the weighted average of the XANES of FeTe and FeSe binaries reproduce well the observed trend in the experimental spectra of the ternary systems. This suggests that the FeTe1−x Sex is characterized by an inhomogeneous local electronic structure, resulting from a random-alloy like local atomic structure. The calculated unoccupied Fe d-density of states at the Fermi level increases monotonically with Te content unlike the observed change in T c with Te content. T c increases with increasing Te content up to x=0.5; however, the superconductivity is suppressed in the FeTe due to magnetic order, which is not considered in these calculations.
Cu K-edge X-ray absorption fine structure (XAFS) on La 2 CuO 4.1 has been used to study the radia... more Cu K-edge X-ray absorption fine structure (XAFS) on La 2 CuO 4.1 has been used to study the radial Cu-O distribution function across the superconducting transition. Fits to the isolated Cu-O XAFS signal show the presence of a non-Gaussian distribution function for temperatures away from the superconducting transition temperature. However, this distribution becomes more harmonic in the vicinity of the superconducting transition temperature T c. The results provide evidence for the coupling between the local atomic dynamics and the particles involved in the superconductivity.
ABSTRACT The mixed valence perovskites La_1-xA_xMnO3 (A=Ca, Sr, Ba, etc.) have been the subject o... more ABSTRACT The mixed valence perovskites La_1-xA_xMnO3 (A=Ca, Sr, Ba, etc.) have been the subject of intense study for at least 40 years because of their intriguing transport, magnetic and structural properties . These materials are ferromagnetic conductors for 0.2 < x < 0.5 and insulators outside of this region. Previous microscopic models of ferromagnetism in these materials have been based on Zener's double exchange mechanism. The lattice was assumed to be rigid and ferromagnetism was thought to be induced by a spin coupling of the Mn^4+ nearest neighbor sites mediated by the conduction electrons. Utilizing XAFS analysis of the Mn K-edge spectrum in these materials, we have found that below Tc the nearest neighbor Mn-O distribution is a single peak. Above Tc the Mn-O distribution was found to consist of two or more components. This observation is consistent with the formation of magnetopolarons above Tc as predicted by recent models. In addition, evidence was found for large static Jahn-Teller distortions of pairs of Mn-O bonds in the octahedra about the Mn sites which produce a natural layering and enhance the formation of magnetopolarons. The Mn and La/A sites were found to be highly ordered as predicted by x-ray diffraction measurements.
Extended X-Ray Absorption Fine Structure measurements of the K-edges of Cd, Te and In were perfor... more Extended X-Ray Absorption Fine Structure measurements of the K-edges of Cd, Te and In were performed in CdTe:In at an Indium concentration of 10 atomic percent. A first set of measurements were performed cooling the sample to 80 K in the dark. After a five minute illumination of the sample, dark conditions were restored and a second set of measurements
Acta Crystallographica Section E Structure Reports Online, 2011
The title compound, (C 16 H 36 N) 3 [Th(NCS) 4 (NO 3) 3 ], was obtained from the reaction of Th(N... more The title compound, (C 16 H 36 N) 3 [Th(NCS) 4 (NO 3) 3 ], was obtained from the reaction of Th(NO 3) 4 Á5H 2 O with (Bu 4 N)(NCS). The Th IV atom is in a ten-coordinate environment of irregular geometry, being bound to the N atoms of the four thiocyanate ions and to three bidentate nitrate ions. The average Th-N and Th-O bond lengths are 2.481 (10) and 2.57 (3) Å , respectively.
Journal of Superconductivity and Novel Magnetism, 2010
We report x-ray absorption fine structure (XAFS) measurements at the Nb K-edge of a Nb 3 Sn singl... more We report x-ray absorption fine structure (XAFS) measurements at the Nb K-edge of a Nb 3 Sn single crystal, for temperatures across the martensitic structural transition temperature T m. The Fourier transform amplitude of the peak associated with the second neighbor Nb-Nb and Nb-Sn pairs exhibits hysteresis across the martensitic transition under cooling and heating the sample across the transition. In contrast no such behavior was found for the Nb-Nb nearest neighbor distribution. The observed hysteresis can be attributed to the second neighbor Nb-Nb pairs as only the Debye-Waller factor of these pairs exhibits such a behavior. These results are consistent with a first-order phase transition, which has been previously proposed, and which suggests the possibility of an inhomogeneous ground state similar to other high-temperature superconductors.
Solubility, migration, and bioavailability of plutonium is lacunar because experimental evidences... more Solubility, migration, and bioavailability of plutonium is lacunar because experimental evidences are missing. We report here on X-ray Absorption Spectroscopy of plutonium in natural seawater. The observed valence state is +IV and its speciation corresponds to PuO2 type colloids. Furthermore, aging of the solution shows a gradient of ordering from hydroxide colloidal species to more crystalline PuO2 colloids.
Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1 À x , using a... more Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1 À x , using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K-edge XANES measurements in the "pre-edge" region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe-Se and Fe-Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSe x Te 1 À x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSe x Te 1 À x. Additionally, we have calculated projected electronic density of d-states for the Fe atom, revealing increased spectral weight in the "pre-edge" region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d-density of states for the Fermi level, N(ε F), for high Te content is consistent with the suppression of superconductivity in the title system. & 2014 Elsevier Ltd. All rights reserved. calculated the Fe d-density of states (DOS) in the vicinity of the Fermi energy of this system, using the same computational method. We have performed calculations in real space, where no translational symmetry is invoked. We note that systems with compositional disorder exhibit a broken translational symmetry, Contents lists available at ScienceDirect
This report was prepared as an account of work sponsored by an agency of the United States Govern... more This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. By acceptance of thisarticle,the publisher recognized that theU S Government retainsa nonexclusive, royalty-free licensetopublishor reproduce thepublished formof thiso._n_ibution or to allowotherstodo soforU S Government purposes. TheLosAlamos National Laboratory requests thatthe publisher identifythisarticle asworkperformed underthe auspices of theU S Department of Energy.
Coexisting electronic correlations and electron-phonon interactions have been proposed to lead to... more Coexisting electronic correlations and electron-phonon interactions have been proposed to lead to dynamic polaron-tunneling behavior for the axial oxygen in YBa2Cu307. Emphasizing nonlinear and nonadiabatic effects, we show that this description leads to distinctive predictions consistent with structural, optical, and inelastic neutron-scattering data in the axial direction.
ABSTRACT Polarized Cu—K edge XAFS (X-ray absorption fine structure) on La2CuO4.1 indicate that th... more ABSTRACT Polarized Cu—K edge XAFS (X-ray absorption fine structure) on La2CuO4.1 indicate that the radial distribution function of the copper in plane oxygen pairs is a two-site distribution, in agreement with the results found by Bianconi et al. for temperatures below the appearance of a pseudogap. Additionally we find evidence of a change in this distribution across the superconducting transition, suggesting coupling between the local lattice structure and the charged particles involved in the superconductivity.
We performed near edge x-ray absorption spectroscopy (XANES) measurements on the Arsenic K-edge o... more We performed near edge x-ray absorption spectroscopy (XANES) measurements on the Arsenic K-edge of As(III) in solution under acidic and basic conditions, after exposure of the solutions to air. Spectra were recorded for increasing exposure times to the x-rays used to perform absorption spectroscopy measurements. We did not find changes for the solution under acidic conditions, while we observed significant changes in the case of solution under alkaline conditions. In order to interpret these changes, we compared the obtained spectra with XANES spectra of As(III) and As(V) solutions under alkaline conditions, not exposed to air, and used as standards. Principal component fits using these standards indicate an accelerated conversion of As(III) to As(V) due to the exposure to x-rays.
The effect of isotopic substitution in the excitation spectrum of a model polaronic system is pre... more The effect of isotopic substitution in the excitation spectrum of a model polaronic system is presented. To study this effect we use a three-site many-body Hamiltonian, with two phonon modes, which includes electronic correlations and electron-phonon interactions. Under isotopic substitution, the shift of the lowest excitation energy changes sign for intermediate electron-phonon coupling, coinciding with the onset of polaronic behavior. This manifests as a strong change of the dynamics of polaron tunneling, a behavior opposite to that found in purely phonon excitations. Additionally, a small change in the static polaronic distortion appears under isotopic substitution. This change in the local structure has opposite signs for low and intermediate electron-phonon coupling compared to that found in the strong-coupling limit. ͓S0163-1829͑99͒08013-3͔ PHYSICAL REVIEW B
X-ray pair distribution function (pdf) and U L 3 extended x-ray absorption fine structure (EXAFS)... more X-ray pair distribution function (pdf) and U L 3 extended x-ray absorption fine structure (EXAFS) and neutron pdf measurements that give identical results for UO 2 show U(VI)-oxo moieties with x rays for mixed valence U 4 O 9 and U 3 O 7 , in contrast to the neutron data that indicate only U(V) sites with no short U-O bonds as well as other differences. In addition, although the EXAFS spectra of UO 2 are essentially identical at 30, 100, and 200 K, those of the UO 2+x compounds exhibit different nearest-neighbor U-O distributions at each temperature. Further tunneling polaron-type behavior is found in the broadening of the features of the O K-edge x-ray absorption spectra (XAS) of the UO 2+x compounds. Raman spectra of powders also show a large increase in scattering cross section with increasing O content that would originate in a change in the electronic structure that increases the overall polarizability. The XAS and Raman also show that U 4 O 9 does not behave as a linear combination of the UO 2 and U 3 O 7 fluorite endpoints. The properties induced by mobile rather than static charged quasiparticles were explored by optical pumping of the metal-to-metal charge-transfer transition. The temperature dependence of 4.71 eV pump-1.57 eV probe reflectivity on UO 2 that initially populates the U 6d-dominated portion of the upper Hubbard band (UHB) shows a sharp 28-μsec lifetime peak at 25 K that may be associated with the fluctuations of its antiferromagnetic transition. Pumping at 3.14 eV into the 5f-dominated portion of the UHB shows an analogous 2.8-μsec peak but also a plateau bracketing this peak that ends in a cusp at 50-60 K and an abrupt change in the hardening rate of a novel 12-15 GHz phonon that is the signature for the quasiparticle quantum phase. The different results for the different excitation channels indicate a highly specific nonthermal relaxation mechanism. These results constitute the first observation of a distinct phase of photoinduced quasiparticles that is sufficiently coupled to the lattice to undergo a gap-opening transition. When the intragap state is probed with a terahertz time domain spectroscopy (TTDS) measurement 33 psec after a 3.14 excitation pulse, it shows increased absorption in the 0.5-1.1 THz range with a decrease in temperature from ∼30 to 10 K instead of the expected decrease, a result consistent with the presence of a condensate. These results are too extreme to originate in the dynamical, nonadiabatic, coupled charge-transfer-phonon/tunneling polaron scenario previously used for doped Mott-Hubbard insulators with intermediate electron-phonon coupling and therefore indicate novel physics. One possibility that could cause all of these behaviors is that a collective, dynamical, charge transfer-coupled Peierls distortion involving the 2 U(V) ↔ U(IV) + U(VI)-oxo excitation occurs coherently over an entire domain to cause the atoms in this domain to condense into a system with Bose-Einstein or Bose-Einstein-Hubbard properties.
Journal of Superconductivity and Novel Magnetism, 2013
ABSTRACT Ab initio Fe K-edge X-ray absorption near edge structure (XANES) calculations on FeTe1−x... more ABSTRACT Ab initio Fe K-edge X-ray absorption near edge structure (XANES) calculations on FeTe1−x Sex , based on its crystallographic structure, are compared with experimental data. The calculated XANES spectra are inconsistent with the observed increase of spectral weight in the preedge region of the experimental spectra on the ternary system in which Te is substituted by Se. However, the weighted average of the XANES of FeTe and FeSe binaries reproduce well the observed trend in the experimental spectra of the ternary systems. This suggests that the FeTe1−x Sex is characterized by an inhomogeneous local electronic structure, resulting from a random-alloy like local atomic structure. The calculated unoccupied Fe d-density of states at the Fermi level increases monotonically with Te content unlike the observed change in T c with Te content. T c increases with increasing Te content up to x=0.5; however, the superconductivity is suppressed in the FeTe due to magnetic order, which is not considered in these calculations.
Cu K-edge X-ray absorption fine structure (XAFS) on La 2 CuO 4.1 has been used to study the radia... more Cu K-edge X-ray absorption fine structure (XAFS) on La 2 CuO 4.1 has been used to study the radial Cu-O distribution function across the superconducting transition. Fits to the isolated Cu-O XAFS signal show the presence of a non-Gaussian distribution function for temperatures away from the superconducting transition temperature. However, this distribution becomes more harmonic in the vicinity of the superconducting transition temperature T c. The results provide evidence for the coupling between the local atomic dynamics and the particles involved in the superconductivity.
ABSTRACT The mixed valence perovskites La_1-xA_xMnO3 (A=Ca, Sr, Ba, etc.) have been the subject o... more ABSTRACT The mixed valence perovskites La_1-xA_xMnO3 (A=Ca, Sr, Ba, etc.) have been the subject of intense study for at least 40 years because of their intriguing transport, magnetic and structural properties . These materials are ferromagnetic conductors for 0.2 < x < 0.5 and insulators outside of this region. Previous microscopic models of ferromagnetism in these materials have been based on Zener's double exchange mechanism. The lattice was assumed to be rigid and ferromagnetism was thought to be induced by a spin coupling of the Mn^4+ nearest neighbor sites mediated by the conduction electrons. Utilizing XAFS analysis of the Mn K-edge spectrum in these materials, we have found that below Tc the nearest neighbor Mn-O distribution is a single peak. Above Tc the Mn-O distribution was found to consist of two or more components. This observation is consistent with the formation of magnetopolarons above Tc as predicted by recent models. In addition, evidence was found for large static Jahn-Teller distortions of pairs of Mn-O bonds in the octahedra about the Mn sites which produce a natural layering and enhance the formation of magnetopolarons. The Mn and La/A sites were found to be highly ordered as predicted by x-ray diffraction measurements.
Extended X-Ray Absorption Fine Structure measurements of the K-edges of Cd, Te and In were perfor... more Extended X-Ray Absorption Fine Structure measurements of the K-edges of Cd, Te and In were performed in CdTe:In at an Indium concentration of 10 atomic percent. A first set of measurements were performed cooling the sample to 80 K in the dark. After a five minute illumination of the sample, dark conditions were restored and a second set of measurements
Acta Crystallographica Section E Structure Reports Online, 2011
The title compound, (C 16 H 36 N) 3 [Th(NCS) 4 (NO 3) 3 ], was obtained from the reaction of Th(N... more The title compound, (C 16 H 36 N) 3 [Th(NCS) 4 (NO 3) 3 ], was obtained from the reaction of Th(NO 3) 4 Á5H 2 O with (Bu 4 N)(NCS). The Th IV atom is in a ten-coordinate environment of irregular geometry, being bound to the N atoms of the four thiocyanate ions and to three bidentate nitrate ions. The average Th-N and Th-O bond lengths are 2.481 (10) and 2.57 (3) Å , respectively.
Journal of Superconductivity and Novel Magnetism, 2010
We report x-ray absorption fine structure (XAFS) measurements at the Nb K-edge of a Nb 3 Sn singl... more We report x-ray absorption fine structure (XAFS) measurements at the Nb K-edge of a Nb 3 Sn single crystal, for temperatures across the martensitic structural transition temperature T m. The Fourier transform amplitude of the peak associated with the second neighbor Nb-Nb and Nb-Sn pairs exhibits hysteresis across the martensitic transition under cooling and heating the sample across the transition. In contrast no such behavior was found for the Nb-Nb nearest neighbor distribution. The observed hysteresis can be attributed to the second neighbor Nb-Nb pairs as only the Debye-Waller factor of these pairs exhibits such a behavior. These results are consistent with a first-order phase transition, which has been previously proposed, and which suggests the possibility of an inhomogeneous ground state similar to other high-temperature superconductors.
Solubility, migration, and bioavailability of plutonium is lacunar because experimental evidences... more Solubility, migration, and bioavailability of plutonium is lacunar because experimental evidences are missing. We report here on X-ray Absorption Spectroscopy of plutonium in natural seawater. The observed valence state is +IV and its speciation corresponds to PuO2 type colloids. Furthermore, aging of the solution shows a gradient of ordering from hydroxide colloidal species to more crystalline PuO2 colloids.
Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1 À x , using a... more Ab initio X-ray absorption near edge structure (XANES) calculations for FeSe x Te 1 À x , using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K-edge XANES measurements in the "pre-edge" region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe-Se and Fe-Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSe x Te 1 À x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSe x Te 1 À x. Additionally, we have calculated projected electronic density of d-states for the Fe atom, revealing increased spectral weight in the "pre-edge" region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d-density of states for the Fermi level, N(ε F), for high Te content is consistent with the suppression of superconductivity in the title system. & 2014 Elsevier Ltd. All rights reserved. calculated the Fe d-density of states (DOS) in the vicinity of the Fermi energy of this system, using the same computational method. We have performed calculations in real space, where no translational symmetry is invoked. We note that systems with compositional disorder exhibit a broken translational symmetry, Contents lists available at ScienceDirect
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