Evidence of a transition to reorientational disorder in the cubic alkali-metal dodecahydro-closo-dodecaborates

Journal Article · Tue Nov 15 00:00:00 EST 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.09.010· OSTI ID:21580084

Verdal, Nina ^[1]; Wu, Hui ^[1]; Udovic, Terrence J ^[1]; Stavila, Vitalie ^[2]; Wei, Zhou; Rush, John J ^[1]

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1. NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-6102 (United States)
2. Sandia National Laboratories, Livermore, CA 94551-0969 (United States)

A neutron powder diffraction and differential scanning calorimetry (DSC) study indicates that Cs{sub 2}B{sub 12}H{sub 12} undergoes a second-order phase transition near 529 K that can be described as a reorientational disordering of the B{sub 12}H{sub 12}{sup 2-} icosahedral anions between two lowest-energy configurations within the cubic structure. Such a disordering requires the addition of another mirror plane to the low-temperature Fm3-bar structural symmetry to become Fm3-bar m. Differential scanning calorimetry measurements suggest the possible persistence of some short-range anion order at and above the transition. Additional DSC measurements of the lighter alkali-metal cubic isomorphs, Rb{sub 2}B{sub 12}H{sub 12} and K{sub 2}B{sub 12}H{sub 12}, also indicate second-order transitions for these compounds near 742 K and 811 K, respectively. These results are suggestive of similar order-disorder phase changes as for Cs{sub 2}B{sub 12}H{sub 12}, although confirmation of their existence requires analogous diffraction measurements. - Graphical Abstract: Cs{sub 2}B{sub 12}H{sub 12} undergoes an order-disorder phase transition near 529 K. Similar transitions are observed for K{sub 2}B{sub 12}H{sub 12} and Rb{sub 2}B{sub 12}H{sub 12}. Highlights: > Diffraction and DSC reveal that Cs{sub 2}B{sub 12}H{sub 12} undergoes a 2nd-order phase transition near 529 K. > This phase transition is from the low-temperature Fm3-bar symmetry to Fm3-bar m at high temperatures. > DSC of Rb{sub 2}B{sub 12}H{sub 12} and K{sub 2}B{sub 12}H{sub 12} indicate 2nd-order transitions near 742 K and 811 K, respectively.

• OSTI ID: 21580084
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 11; Other Information: DOI: 10.1016/j.jssc.2011.09.010; PII: S0022-4596(11)00501-9; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALKALI METALS
ANIONS
CALORIMETRY
CUBIC LATTICES
NEUTRON DIFFRACTION
ORDER-DISORDER TRANSFORMATIONS
SYMMETRY
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0400-1000 K
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
ELEMENTS
IONS
METALS
PHASE TRANSFORMATIONS
SCATTERING
TEMPERATURE RANGE