Laboratory for Developments and Methods

Villigen, Switzerland

Laboratory for Developments and Methods

Villigen, Switzerland
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Svitlyk V.,European Synchrotron Radiation Facility | Chernyshov D.,European Synchrotron Radiation Facility | Pomjakushina E.,Laboratory for Developments and Methods | Krzton-Maziopa A.,Laboratory for Developments and Methods | And 3 more authors.
Inorganic Chemistry | Year: 2011

Temperature-dependent synchrotron powder diffraction on Cs 0.83(Fe0.86Se)2 revealed first-order I4/m to I4/mmm structural transformation around 216 °C associated with a disorder of the Fe vacancies. Irreversibility observed during the transition is likely associated with a mobility of the intercalated alkali atoms. Pressure-dependent synchrotron powder diffraction on Cs0.83(Fe1-ySe) 2, Rb0.85(Fe1-ySe)2, and K 0.8(Fe1-ySe)2 (y ∼ 0.14) indicated that the I4/m superstructure reflections are present up to pressures of 120 kbar. This may indicate that the ordering of the Fe vacancies is present in both superconducting and nonsuperconductive states. © 2011 American Chemical Society.


Pomjakushin V.Yu.,Paul Scherrer Institute | Krzton-Maziopa A.,Laboratory for Developments and Methods | Pomjakushina E.V.,Laboratory for Developments and Methods | Conder K.,Laboratory for Developments and Methods | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2012

The crystal and magnetic structures of the superconducting iron-based chalcogenides Rb yFe 2xSe 2 have been studied by means of single-crystal synchrotron x-ray and high-resolution neutron powder diffraction in the temperature range 2-570K. The ground state of the crystal is an intrinsically phase-separated state with two distinct-by-symmetry phases. The main phase has the iron vacancy ordered √5 × √5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have √5 × √5-type of ordering and has a smaller in-plane lattice constant a and larger tetragonal c-axis and can be well described by assuming the parent average vacancy disordered structure (I4/mmm space group) with the refined stoichiometry Rb 0.60(5)(Fe 1.10(5)Se) 2. The minority phase amounts to 8-10% mass fraction. The unit cell volume of the minority phase is 3.2% smaller than the one of the main phase at T=2K and has quite different temperature dependence. The minority phase merges with the main vacancy ordered phase on heating above the phase separation temperature T P=475K. The spatial dimensions of the phase domains strongly increase above T P from 1000 to >2500 Å due to the integration of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at a temperature T=488K, close to T P, for a long time drastically reduces the amount of the minority phase. © 2012 IOP Publishing Ltd.


Bosak A.,European Synchrotron Radiation Facility | Svitlyk V.,European Synchrotron Radiation Facility | Svitlyk V.,University of Munster | Krzton-Maziopa A.,Laboratory for Developments and Methods | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A xFe 2-ySe 2 (A = K, Rb, Cs) superconductors are frequently complex mixtures of phases even in the form usually described as a single crystal. Phases, resulting from phase separation, metrically are very similar, so their detailed characterization is a delicate task, and the existing data are typically scarce. We characterize the room-temperature phase-separated state of Cs 0.8Fe 1.6Se 2 in reciprocal space by means of single-crystal diffraction of synchrotron radiation. Using the arguments of commensurability and detailed analysis of twinning patterns, we augment the previous findings by quantifying the intergrowth state, consisting of the tetragonal phase with ordered Fe vacancies and the minor disordered phase. Compared to the main phase, the minor one is compressed in the tetragonal a-b plane and expanded along the c direction; a set of modulated Bragg rods evidences a planar disorder. Fourfold splitting of the rods and main Bragg peaks implies a rotational twinning; close inspection of the lattice metric indicates that the symmetry of the minor phase is not higher than monoclinic, with a deviation from the orthogonal basis of ∼0.25°. © 2012 American Physical Society.


Pomjakushin V.Yu.,Paul Scherrer Institute | Sheptyakov D.V.,Paul Scherrer Institute | Pomjakushina E.V.,Laboratory for Developments and Methods | Krzton-Maziopa A.,Laboratory for Developments and Methods | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Neutron and x-ray powder and single crystal synchrotron diffraction of CsyFe2-xSe2 show the presence of superstructure reflections with propagation vector k=[25,15,1] with respect to the average crystal structure I4/mmm (a∼4,c∼15 Å). The propagation vector star corresponds to the 5 times bigger unit cell given by transformation A=2a+b, B=-a+2b, C=c. A solution for the atomic structure is found in the space group I4/m with an ordered pattern of iron vacancies corresponding to the iron deficiency x=0.29 and Cs stoichiometry y=0.83. The superstructure satellites are more pronounced in the neutron diffraction patterns suggesting that they can have some magnetic contribution. We have sorted out all possible symmetry adapted magnetic configurations and found that the presence of antiferromagnetic ordering with the ordered magnetic moment of Fe with 2μB does not contradict the experimental data. However, the solutions space is highly degenerate and we cannot choose a specific solution. Instead we propose possible magnetic configurations with the Fe magnetic moments in (ab) plane or along c axis. The superstructure is destroyed above Ts 500 K by a first-order-like transition. © 2011 American Physical Society.


Pikart P.,TU Munich | Hugenschmidt C.,TU Munich | Horisberger M.,Laboratory for Developments and Methods | Matsukawa Y.,Tohoku University | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Defect-sensitive and element-selective measurements on ultrathin chrome, copper, and gold layers embedded in aluminium are presented using coincident Doppler broadening spectroscopy (CDBS) with a monoenergetic positron beam. The amounts of positrons implanted in the layers of different thicknesses are calculated and compared with the experimentally gained fractions of positrons annihilating in the buried layers. A high sensitivity was already reached at an Au layer of only 2 nm thickness embedded below 200 nm Al, which was attributed to the highly efficient positron trapping in the Au layer and Au clusters. An implantation and diffusion model describes this high sensitivity for positron trapping layers. A quantum-well model of the positron wave function limits the trapping to gold clusters of a radius larger than 0.23 nm. This result was confirmed experimentally and validated with complementary TEM measurements. © 2011 American Physical Society.


Penkala B.,Charles Gerhardt Institute | Penkala B.,Saint - Gobain | Aubert D.,Saint - Gobain | Kaper H.,Saint - Gobain | And 3 more authors.
Catalysis Science and Technology | Year: 2015

Ceria-based materials are today the most prominently used catalyst supports for CO oxidation and NOx reduction in three-way catalytic converters (TWCs) worldwide. Acting as oxygen buffer compounds, the underlying reaction mechanism and especially the distinct role of surface and lattice oxygen for catalytic reactions are still under debate. This is partially related to the complexity of the real CeO2 surface containing important amounts of water and carbonates. Combining TG-MS, Raman spectroscopic experiments and isotope labeling pulse temperature programmed oxidation reaction (ILPOR), coupled with mass spectrometric analysis of 18O-doped ceria, we explored here the oxygen uptake/release behavior under operando conditions, together with the catalytic activity related to surface and/or lattice oxygen mobility and exchange. Specific changes in the lattice dynamics induced by 18/16O isotope exchange were analyzed by Raman spectroscopy, allowing the temperature-dependent onset of lattice oxygen mobility and isotope exchange behavior to be studied selectively. For Pt-supported nano-ceria, we evidenced high catalytic performance for CO oxidation, activated slightly above ambient conditions without significant lattice oxygen participation. The distinct role of surface and lattice oxygen in the catalytic reaction of ceria catalysts is discussed as a function of temperature, grain size, Gd doping and Pt impregnation. © The Royal Society of Chemistry.


Mansart B.,Ecole Polytechnique Federale de Lausanne | Cottet M.J.G.,Ecole Polytechnique Federale de Lausanne | Mancini G.F.,Ecole Polytechnique Federale de Lausanne | Jarlborg T.,University of Geneva | And 16 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The strength of the electron-phonon coupling parameter and its evolution throughout a solid's phase diagram often determines phenomena such as superconductivity, charge- and spin-density waves. Its experimental determination relies on the ability to distinguish thermally activated phonons from those emitted by conduction band electrons, which can be achieved in an elegant way by ultrafast techniques. Separating the electronic from the out-of-equilibrium lattice subsystems, we probed their reequilibration by monitoring the transient lattice temperature through femtosecond x-ray diffraction in La2-xSrxCuO4 single crystals with x=0.1 and 0.21. The temperature dependence of the electron-phonon coupling is obtained experimentally and shows similar trends to what is expected from the ab initio calculated shape of the electronic density of states near the Fermi energy. This study evidences the important role of band effects in the electron-lattice interaction in solids, in particular, in superconductors. © 2013 American Physical Society.


Penkala B.,Charles Gerhardt Institute | Penkala B.,Saint - Gobain | Aubert D.,Saint - Gobain | Kaper H.,Saint - Gobain | And 3 more authors.
Catalysis Science and Technology | Year: 2015

Ceria-based materials are today the most prominently used catalyst supports for CO oxidation and NOx reduction in three-way catalytic converters (TWCs) worldwide. Acting as oxygen buffer compounds, the underlying reaction mechanism and especially the distinct role of surface and lattice oxygen for catalytic reactions are still under debate. This is partially related to the complexity of the real CeO2 surface containing important amounts of water and carbonates. Combining TG-MS, Raman spectroscopic experiments and isotope labeling pulse temperature programmed oxidation reaction (ILPOR), coupled with mass spectrometric analysis of 18O-doped ceria, we explored here the oxygen uptake/release behavior under operando conditions, together with the catalytic activity related to surface and/or lattice oxygen mobility and exchange. Specific changes in the lattice dynamics induced by 18/16O isotope exchange were analyzed by Raman spectroscopy, allowing the temperature-dependent onset of lattice oxygen mobility and isotope exchange behavior to be studied selectively. For Pt-supported nano-ceria, we evidenced high catalytic performance for CO oxidation, activated slightly above ambient conditions without significant lattice oxygen participation. The distinct role of surface and lattice oxygen in the catalytic reaction of ceria catalysts is discussed as a function of temperature, grain size, Gd doping and Pt impregnation. This journal is © The Royal Society of Chemistry.


Pomjakushin V.Yu.,Paul Scherrer Institute | Sheptyakov D.V.,Paul Scherrer Institute | Pomjakushina E.V.,Laboratory for Developments and Methods | Conder K.,Laboratory for Developments and Methods | Balagurov A.M.,Joint Institute for Nuclear Research
Journal of Physics Condensed Matter | Year: 2010

High resolution neutron diffraction shows that the mesoscopic separation into ferromagnetic (FM) and antiferromagnetic (AFM) phases and the FM transition temperature TC in the perovskite manganite (La 1 - yPry)0.7Ca0.3MnO3 strongly depend on the quenched correlated disorder. The different disorder strengths are achieved by different procedures of the sample synthesis and are quantitatively characterized by the microstrain-type diffraction peak broadening. The system shifts to predominantly a one-phase state with smaller TC as the correlated disorder strength is decreased, supporting the viewpoint that the origin of phase separation in the indicated manganite system is the correlated quenched disorder. The ground state of an ultimately chemically homogeneous sample is FM-like containing about 20% of the AFM minority phase. This FM-like state can be readily transformed to the AFM-like one having < 20% of the FM phase by the decrease of the effective charge carrier bandwidth via oxygen isotope substitution. © 2010 IOP Publishing Ltd.


Pashkevich Y.,Ukrainian Academy of Sciences | Gnezdilov V.,Ukrainian Academy of Sciences | Lemmens P.,TU Braunschweig | Shevtsova T.,Ukrainian Academy of Sciences | And 6 more authors.
Low Temperature Physics | Year: 2016

We report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K over a wide temperature region 3-500 K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed RbδFe2Se2 (122) conductive phase. The superconducting gap with dx2-y2 symmetry has been detected in our spectra. In the range 0-600 cm-1 we observe a weak but highly polarized B1g-type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M0.8+xFe1.6+ySe2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic RbδFe2Se2 phase and the insulating Rb2Fe4Se5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb0.8+xFe1.6+ySe2. Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb2Fe4Se5 phases.

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