Comparison of Anion and Cation Dynamics in a Carbon-Substituted closo-Hydroborate Salt: 1H and 23Na NMR Studies of Solid-Solution Na2(CB9H10)(CB11H12)
A. V. Soloninin, R. V. Skoryunov, O. A. Babanova, A. V. Skripov, Mirjana NMN Dimitrievska, Terrence J. Udovic
The hexagonal mixed-anion solid solution Na2(CB9H10)(CB11H12) shows the highest room-temperature ionic conductivity among all known Na-ion conductors. To study the dynamical properties of this compound, we have measured ghe 1H and 23Na nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in Na2(CB9H10)(CB11H12) over the temperature range of 80 K to 435 K. It is found that the diffusive motion of Na+ ions can be described in terms of two jump processes: the fast localized motion within the pairs of tetrahedral interstitial sites of the hexagonal close-packed lattice formed by large anions and the slower jump process via octahedral sites leading to long-range diffusion. Below 350 K, the slower Na+ jump process is characterized by the activation energy of 353(11) meV. Although Na+ mobility in Na2(CB9H10)(CB11H12) found from our NMR experiments is higher than in other ionic conductors, it appears to be an order-of-magnitude lower than that expected on the basis of the conductivity measurements. This result suggests that the complex diffusion mechanism and/or correlations between Na+ jumps should be taken into account. The measured 1H spin-lattice relaxation rates for Na2(CB9H10)(CB11H12) are consistent with a coexistence of at least two anion reorientational jump processes occurring at different frequency scales. Near room temperature, both reorientational processes are found to be faster than the Na+ jump process responsible for the long-range diffusion.
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Comparison of Anion and Cation Dynamics in a Carbon-Substituted closo-Hydroborate Salt: <sub>1</sub>H and <sup>23</sup>Na NMR Studies of Solid-Solution Na<sub>2</sub>(CB<sub>9</sub>H<sub>10</sub>)(CB<sub>11</sub>H<sub>12</sub>), Journal of Alloys and Compounds, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=927728
(Accessed May 16, 2021)