Structural Behavior of Li<sub>2</sub>B<sub>10</sub>H<sub>10</sub>

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.