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Structure and Dynam...
Structure and Dynamics for LiBH4-LiCl Solid Solutions
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Arnbjerg, Lene M. (författare)
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Ravnsbaek, Dorthe B. (författare)
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Filinchuk, Yaroslav (författare)
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Vang, Ronnie T. (författare)
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- Cerenius, Yngve (författare)
- Lund University,Lunds universitet,MAX IV-laboratoriet,MAX IV Laboratory
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Besenbacher, Flemming (författare)
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Jorgensen, Jens-Erik (författare)
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Jakobsen, Hans Jorgen (författare)
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Jensen, Torben R. (författare)
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(creator_code:org_t)
- 2009-11-18
- 2009
- Engelska.
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:24, s. 5772-5782
- Relaterad länk:
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http://dx.doi.org/10...
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https://pubs.acs.org...
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https://lup.lub.lu.s...
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https://doi.org/10.1...
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Abstract
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- A Surprisingly high degree of structural and compositional dynamics is observed in the system LiBH4-LiCl as a function of temperature and time. Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data reveals that Cl- readily substitutes for BH4- in the Structure of LiBH4. Prolonged heating a sample of LiBH4-LiCl (1:1 molar ratio) above the phase transition temperature and below the melting point (108 < T < 275 degrees C) can produce highly chloride substituted hexagonal lithium borohydride, h-Li(BH4)(l-x)Cl-x, e.g., x similar to 0.42, after heating from room temperature (RT) to 224 degrees C at 2.5 degrees C/min. LiCl has a higher solubility in h-LiBH4 its compared to orthorhombic lithium borohydride, o-LiBH4, which is illustrated by a LiBH4-LiCl (1:1) sample equilibrated at 245 degrees C for 24 days and left at RT for another 13 months. Rietveld refinement reveals that this sample contains o-Li(BH4)(0.91)Cl-0.09 and LiCl. This illustrates a significantly faster dissolution of LiCl in h-LiBH4 its compared to a slower segregation of LiCl from o-LiBH4, which is also demonstrated by in situ SR-PXD from three cycles of heating and cooling of the same Li(BH4)(0.91)Cl-0.09 sample. The substitution of the smaller Cl- for the larger BH4- ion is clearly observed as a reduction in the unit cell volume as a function of time and temperature. A significant stabilization of h-LiBH4 is found to depend on the degree of anion substitution. Variable temperature solid-state magic-angle spinning (MAS) Li-7 and B-13 NMR experiments oil pure LiBH4 show an increase in full width at half maximum (fwhm) when approaching the phase transition from o- to h-LiBH4, which indicates an increase of the relaxation rate (i.e. T-2 decreases). A less pronounced effect is observed for ion-substituted Li(BH4)(1-x)Cl-x, 0.09 < x < 0.42. The MAS NMR experiments also demonstrate a higher degree of motion in the hexagonal phase, i.e., fwhm is reduced by more than a Factor of 10 at the o- to h-LiBH4 phase transition.
Ämnesord
- NATURVETENSKAP -- Kemi -- Materialkemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Materials Chemistry (hsv//eng)
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