Structural Behavior of Li<sub>2</sub>B<sub>10</sub>H<sub>10</sub>
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Abstract
On
the basis of X-ray and neutron powder diffraction, first-principles
calculations, and neutron vibrational spectroscopy, Li<sub>2</sub>B<sub>10</sub>H<sub>10</sub> was found to exhibit atypical hexagonal
symmetry to best stabilize the ionic packing of the relatively small
Li<sup>+</sup> cations and large ellipsoidal B<sub>10</sub>H<sub>10</sub><sup>2–</sup> anions. Moreover, differential scanning calorimetry
and neutron-elastic-scattering fixed-window scans suggested that Li<sub>2</sub>B<sub>10</sub>H<sub>10</sub>, similar to its polyhedral cousin
Li<sub>2</sub>B<sub>12</sub>H<sub>12</sub>, undergoes an order–disorder
phase transition near 640
K. These results provide valuable structural information pertinent
to understanding the potential role that Li<sub>2</sub>B<sub>10</sub>H<sub>10</sub> plays during LiBH<sub>4</sub> dehydrogenation–rehydrogenation
as well as its prospects as a superionic Li<sup>+</sup> cation conductor
