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Full-Text Articles in Physics

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Apr 2013

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Conference Papers, Posters, and Presentations

The phonon dispersion was measured at room temperature (above the Néel temperature TN) along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Magnetostructural effects are well documented in the AFe2As2-based (A = Ca, Sr, Ba, Eu) systems. Only recently have single crystals of LaFeAsO become available. The experimentally observed splitting between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 materials are confirmed to be present in LaFeAsO. This is discussed ...


Flux Requirements For The Growth Of Rfeaso (R = Rare Earth) Superconductors, J.-Q. Yan, Brandt A. Jensen, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso Feb 2011

Flux Requirements For The Growth Of Rfeaso (R = Rare Earth) Superconductors, J.-Q. Yan, Brandt A. Jensen, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Publications

Millimeter-sized LaFeAsO single crystals have been successfully grown out of NaAs flux starting with (LaAs+1/2Fe2O3):20NaAs. The factors which allow the growth of these crystals out of NaAs but not out of many other fluxes, such as FeAs, have been investigated. X-ray powder diffraction found that NaAs synthesized for the growth ofRFeAsO superconductors has monoclinic LiAs structure. Thermal analysis confirmed that NaAs melts congruently at about 600 °C. The ability to extract RFeAsO crystals from this NaAs flux suggests that NaAs has a significant oxygen solubility, possibly due to the formation of ...


Flux Growth At Ambient Pressure Of Millimeter-Sized Single Crystals Of Lafeaso, Lafeaso1−Xfx, And Lafe1−Xcoxaso, J.-Q. Yan, Shibabrata Nandi, Jerel L. Zarestky, W. Tian, Andreas Kreyssig, Brandt A. Jensen, A. Kracher, Kevin W. Dennis, Robert J. Mcqueeney, Alan I. Goldman, R. William Mccallum, Thomas A. Lograsso Dec 2009

Flux Growth At Ambient Pressure Of Millimeter-Sized Single Crystals Of Lafeaso, Lafeaso1−Xfx, And Lafe1−Xcoxaso, J.-Q. Yan, Shibabrata Nandi, Jerel L. Zarestky, W. Tian, Andreas Kreyssig, Brandt A. Jensen, A. Kracher, Kevin W. Dennis, Robert J. Mcqueeney, Alan I. Goldman, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Publications

Millimeter-sized single crystals of LaFeAsO, LaFeAsO1−xFx, and LaFe1−xCoxAsO were grown in NaAs flux at ambient pressure. The detailed growth procedure and crystal characterizations are reported. The as-grown crystals have typical dimensions of3×4×0.05–0.3 mm3 with the crystallographic c-axis perpendicular to the plane of the platelike single crystals. Various characterizations confirmed the high quality of our LaFeAsO crystals. Co and F were introduced into the lattice leading to superconductingLaFe1−xCoxAsO and LaFeAsO1−xFx single crystals, respectively. This growth protocol ...


In Situ High Energy X-Ray Synchrotron Diffraction Study Of The Synthesis And Stoichiometry Of Lafeaso And Lafeaso1−Xfy, R. William Mccallum, J.-Q. Yan, Gustav E. Rustan, E. D. Mun, Yogesh Singh, S. Das, R. Nath, Sergey L. Bud'ko, Kevin W. Dennis, David C. Johnston, Paul C. Canfield, Matthew J. Kramer, Andreas Kreyssig, Thomas A. Lograsso, Alan I. Goldman Jun 2009

In Situ High Energy X-Ray Synchrotron Diffraction Study Of The Synthesis And Stoichiometry Of Lafeaso And Lafeaso1−Xfy, R. William Mccallum, J.-Q. Yan, Gustav E. Rustan, E. D. Mun, Yogesh Singh, S. Das, R. Nath, Sergey L. Bud'ko, Kevin W. Dennis, David C. Johnston, Paul C. Canfield, Matthew J. Kramer, Andreas Kreyssig, Thomas A. Lograsso, Alan I. Goldman

Ames Laboratory Publications

The reaction path for the synthesis of LaFeAsO and LaFeAsO1−xFy by solid state reaction was studied by in situ high temperature x-ray diffraction technique and differential thermal analysis in the temperature interval 100 °C ⩽ T ⩽ 1150 °C. Starting with LaAs, Fe2O3, Fe, and LaF3 as precursors, the results show that the synthesis is characterized by three temperature intervals: (1) Below 500 °C the sequential reduction of Fe2O3 and Fe3O4takes place through the oxidization of LaAs. Below 400 °C, Fe2O3 is reduced to ...