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Title: Carbon Incorporation and Anion Dynamics as Synergistic Drivers for Ultrafast Diffusion in Superionic LiCB 11H 12 and NaCB 11H 12

The disordered phases ofLiCB 11H 12 and NaCB 11H 12 possess superb superionic conductivities that make them suitable as solid electrolytes. In these materials, cation diffusion correlates with high orientational mobilities of the CB 11H 12 - anions; however, the precise relationship has yet to be demonstrated. In this work, ab initio molecular dynamics and quasielastic neutron scattering are combined to probe anion reorientations and their mechanistic connection to cation mobility over a range of timescales and temperatures. It is found that anions do not rotate freely, but rather transition rapidly between orientations defined by the cation sublattice symmetry. The symmetry-breaking carbon atom in CB 11H 12 - also plays a critical role by perturbing the energy landscape along the instantaneous orientation of the anion dipole, which couples fluctuations in the cation probability density directly to the anion motion. Anion reorientation rates exceed 3 x 10 10 s -1, suggesting the underlying energy landscape fluctuates dynamically on diffusion-relevant timescales. Furthermore, carbon is found to modify the orientational preferences of the anions and aid rotational mobility, creating additional symmetry incompatibilities that inhibit ordering. The results suggest that synergy between the anion reorientational dynamics and the carbon-modified cation-anion interaction accounts for themore » higher ionic conductivity in CB 11H 12 - salts compared with B 12H 12 2-.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3] ;  [2] ;  [1] ;  [4] ;  [5] ;  [6] ; ORCiD logo [2]
  1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Univ. of Antwerp (Belgium)
  4. Ural Division of the Russian Academy of Sciences, Ekaterinburg (Russian Federation)
  5. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  6. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
Publication Date:
Report Number(s):
NREL/JA-5900-71080
Journal ID: ISSN 1614-6832
Grant/Contract Number:
AC36-08GO28308; AC52-07NA27344; AC04-94AL85000; 15-ERD-022
Type:
Accepted Manuscript
Journal Name:
Advanced Energy Materials
Additional Journal Information:
Journal Volume: 8; Journal Issue: 8; Journal ID: ISSN 1614-6832
Publisher:
Wiley
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Hydrogen and Fuel Cell Technologies Program (EE-3F); USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ab initio molecular dynamics; closo-borates; quasielastic neutron scattering; solid electrolytes; superionic
OSTI Identifier:
1425573
Alternate Identifier(s):
OSTI ID: 1422013