Browsing by Author "Buckley, CE"

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    Fluorine substitution in magnesium hydride as a tool for thermodynamic control
    (American Chemical Society, 2020-04-01) Humphries, TD; Yang, J; Mole, RA; Paskevicius, M; Bird, JE; Rowles, MR; Tortoza, MS; Sofianos, MV; Yu, DH; Buckley, CE
    Metal hydrides continue to vie for attention as materials in multiple technological applications including hydrogen storage media, thermal energy storage (TES) materials, and hydrogen compressors. These applications depend on the temperature at which the materials desorb and reabsorb hydrogen. Magnesium hydride is ideal as a TES material, although its practical operating temperature is capped at ∼450 °C because of material degradation and high operating pressure. Fluorine substitution for hydrogen in magnesium hydride has previously been shown to increase the operating temperature of the metal hydride while limiting degradation, although full characterization is required before technological application can be ensured. The present study characterizes Mg(HxF1-x)2 solid solutions (x = 1, 0.95, 0.70, 0.85, 0.50, and 0) by inelastic neutron spectroscopy, powder X-ray diffraction, and thermal conductivity measurements, with the results being verified by density functional theory. For each experiment, a clear trend is observed throughout a series of solid solutions, showing the possibility of tuning the properties of MgH2. As F- substitution increases, the average Mg-H(F) bond distance elongates along the axial positions of the Mg-H(F) octahedra. Overall, this leads to an increase in Mg-H bond strength and thermal stability, improving the viability of Mg-H-F as potential TES materials. © 2020 American Chemical Society.
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    Kinetic limitations in the Mg-Si-H system
    (Pergamon-Elsevier Science LTD, 2011-08-01) Paskevicius, M; Sheppard, DA; Chaudhary, AL; Webb, CJ; Gray, EM; Tian, HY; Peterson, VK; Buckley, CE
    Magnesium silicide (Mg(2)Si) has attracted interest as a hydrogen storage material due to favorable thermodynamics (Delta H(desorption) = 36 kJ/mol H(2)) for room temperature operation. To date, direct hydriding of Mg(2)Si under hydrogen gas to form MgH(2) and Si has only been attempted at low pressure and has been hindered by poor kinetics of absorption. In this paper we study the dehydrogenation reaction with in-situ neutron powder diffraction and present results of our attempts to hydrogenate Mg(2)Si under both hydrogen and deuterium gas up to temperatures of 350 degrees C and pressures of 1850 bar. Even under these extreme absorption conditions Mg(2)Si does not absorb any measureable quantity of hydrogen or deuterium. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd
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    Resonant soft x-ray powder diffraction study to determine the orbital ordering in a-site-ordered SmBaMn2O6
    (American Physical Society, 2008-02) García-Fernández, M; Staub, U; Bodenthin, Y; Lawrence, SM; Mulders, AM; Buckley, CE; Weyeneth, S; Pomjakushina, E; Conder, K
    Soft x-ray resonant powder diffraction has been performed at the Mn L-2,L-3 edges of A-site-ordered SmBaMn2O6. The energy and polarization dependences of the (1/4 1/4 0) reflection provide direct evidence for a (x(2) - z(2))/(y(2) - z(2))-type orbital ordering in contrast to single-layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at approximate to 210 K, below which the charge- and orbital-ordered MnO2 sheets show AAAA-type of stacking. The concurring reduction of the ferromagnetic superexchange correlations leads to further charge localization. © 2008, American Physical Society