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Title: Investigation of an unusual low-temperature phase transformation in RbBH{sub 4} by neutron diffraction

To investigate the previously reported low-temperature phase transition in rubidium borohydride (RbBH{sub 4}) near 48.5 K, we carried out neutron powder diffraction and vibrational spectroscopy measurements both above and below this temperature on an isotopically-enriched sample of Rb{sup 11}BD{sub 4}. Our diffraction data reflected an average cubic Fm3{sup ¯}m structure with BD{sub 4}{sup −} anion orientational disorder at all temperatures, with no hint of extra Bragg peaks due to long-range orientational order below the transition temperature as reported by others. These structural results and careful analysis of torsional vibrations in RbBD{sub 4} corroborate the results of prior neutron vibrational spectroscopy measurements suggesting that the low-temperature RbBH{sub 4} structure indeed possesses some orientational ordering of the BH{sub 4}{sup −} anions, but of a shorter-ranged nature insensitive to powder diffraction methods. - The neutron powder diffraction pattern of RbBD{sub 4} below the phase transition temperature (shown here in black) is indistinguishable from that collected above the phase transition temperature. The inset depicts the cubic structure that fits the data at both temperatures. - Highlights: • We investigated the nature of the RbBD{sub 4} phase transition using NVS and NPD. • A change in shape of the RbBD{sub 4} torsion mode was observedmore » across the transition. • The RbBD{sub 4} diffraction pattern across this phase transition was unchanged. • The phase transition in RbBD{sub 4} appears to produce only short-range ordering of BD{sub 4}{sup −}.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [2] ;  [3] ;  [1] ;  [4]
  1. Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)
  2. NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-6102 (United States)
  3. (United States)
  4. Radiation and Isotopes for Health, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)
Publication Date:
OSTI Identifier:
22309015
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 203; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANIONS; BOROHYDRIDES; BRAGG CURVE; CUBIC LATTICES; NEUTRON DIFFRACTION; NEUTRONS; PHASE TRANSFORMATIONS; POWDERS; RUBIDIUM; SPECTROSCOPY; TEMPERATURE RANGE 0065-0273 K; TORSION; TRANSITION TEMPERATURE