Structural and Dynamical Properties of Potassium Dodecahydro-monocarba-closo-dodecaborate: KCB11H12
Artikel i vetenskaplig tidskrift, 2020

MCB11H12 (M: Li, Na) dodecahydro-monocarba-closo-dodecaborate salt compounds are known to have stellar superionic Li+ and Na+ conductivities in their high-temperature disordered phases, making them potentially appealing electrolytes in all-solid-state batteries. Nonetheless, it is of keen interest to search for other related materials with similar conductivities while at the same time exhibiting even lower (more device-relevant) disordering temperatures, a key challenge for this class of materials. With this in mind, the unknown structural and dynamical properties of the heavier KCB11H12 congener were investigated in detail by X-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and AC impedance measurements. This salt indeed undergoes an entropy-driven, reversible, order-disorder transformation and with a lower onset temperature (348 K upon heating and 340 K upon cooling) in comparison to the lighter LiCB11H12 and NaCB11H12 analogues. The K+ cations in both the low-T ordered monoclinic (P2(1)/c) and high-T disordered cubic (Fm (3) over barm) structures occupy octahedral interstices formed by CB11H12- anions. In the low-T structure, the anions orient themselves so as to avoid close proximity between their highly electropositive C-H vertices and the neighboring K+ cations. In the high-T structure, the anions are orientationally disordered, although to best avoid the K+ cations, the anions likely orient themselves so that their C-H axes are aligned in one of eight possible directions along the body diagonals of the cubic unit cell. Across the transition, anion reorientational jump rates change from 6.2 x 10(6) s(-1) in the low-T phase (332 K) to 2.6 x 10(10) s(-1) in the high-T phase (341 K). In tandem, K+ conductivity increases by about 30-fold across the transition, yielding a high-T phase value of 3.2 x 10(-4 )S cm(-1 )at 361 K. However, this is still about 1 to 2 orders of magnitude lower than that observed for LiCB(11)H(12 )and NaCB11H12, suggesting that the relatively larger K+ cation is much more sterically hindered than Li+ and Na+ from diffusing through the anion lattice via the network of smaller interstitial sites.


Mirjana Dimitrievska

National Renewable Energy Laboratory

Ecole Polytechnique Federale de Lausanne (EPFL)

National Institute of Standards and Technology (NIST)

Hui Wu

National Institute of Standards and Technology (NIST)

Vitalie Stavila

Sandia National Laboratories

Olga A. Babanova

Russian Academy of Sciences


Russian Academy of Sciences


Russian Academy of Sciences

Wei Zhou

National Institute of Standards and Technology (NIST)

Benjamin A. Trump

National Institute of Standards and Technology (NIST)

Mikael Andersson

Chalmers, Kemi och kemiteknik, Energi och material, Oorganisk miljökemi 2


Russian Academy of Sciences

Terrence J. Udovic

University of Maryland

National Institute of Standards and Technology (NIST)

Journal of Physical Chemistry C

1932-7447 (ISSN) 1932-7455 (eISSN)

Vol. 124 33 17992-18002


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