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Cation Size and Anion Anisotropy in Structural Chemistry of Metal Borohydrides. The Peculiar Pressure Evolution of RbBH4
Umeå University, Faculty of Science and Technology, Department of Physics.
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2010 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 11, 5285-5292 p.Article in journal (Refereed) Published
Abstract [en]

The pressure evolution of RbBH4 has been characterized by synchrotron powder X-ray diffraction and Raman spectroscopy up to 23 GPa. Diffraction experiments at ambient temperature reveal three phase transitions, at 3.0, 10.4, and 18 GPa (at 2.6, 7.8, and 20 GPa from Raman data), at which the space group symmetry changes in the order Fm-3m(Z=4) → P4/nmm(2) → C222(2) → I-42m(4). Crystal structures and equations of state are reported for all four phases. The three high-pressure structure types are new in the crystal chemistry of borohydrides. RbBH4 polymorphs reveal high coordination numbers (CNs) for cation and anion sites, increasing with pressure from 6 to 8, via an intermediate 4 + 4 coordination. Different arrangements of the tetrahedral BH4 group in the Rb environment define the crystal symmetries of the RbBH4 polymorphs. The structural evolution in the MBH4 series is determined by the cation’s size, as it differs drastically for M = Li (CNs = 4, 6), Na (CN = 6), and Rb. The only structure common to the whole MBH4 family is the cubic one. Its bulk modulus linearly decreases as the ionic radius of M increases, indicating that the compressibility of the material is mainly determined by the repulsive BH4···BH4 interactions.

Place, publisher, year, edition, pages
2010. Vol. 49, no 11, 5285-5292 p.
Keyword [en]
RbBH4, rubidium borohydride, high pressure, X-ray diffraction, XRD, Raman spectroscopy, lattice structure, phase transformation, phase diagram, hydrogen storage
National Category
Inorganic Chemistry Condensed Matter Physics
Research subject
URN: urn:nbn:se:umu:diva-34404DOI: 10.1021/ic100359vISI: 000278110100074OAI: diva2:321476
Supplementary information available at the journal website: Crystallographic Information file: ic100359v_si_001.cif, Raman data and Rietveld XRD refinement profiles: ic100359v_si_002.pdfAvailable from: 2010-06-01 Created: 2010-06-01 Last updated: 2010-07-08Bibliographically approved

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Talyzin, Alexandr V.Sundqvist, Bertil
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