Cation Disorder and Large Tetragonal Supercell Ordering in the Li-Rich Argyrodite Li7Zn0.5SiS6

Leube, Bernhard T, Collins, Christopher M ORCID: 0000-0002-0101-4426, Daniels, Luke M ORCID: 0000-0002-7077-6125, Duff, Benjamin B ORCID: 0000-0002-7398-5002, Dang, Yun ORCID: 0000-0002-0140-0140, Chen, Ruiyong ORCID: 0000-0002-5340-248X, Gaultois, Michael W ORCID: 0000-0003-2172-2507, Manning, Troy D ORCID: 0000-0002-7624-4306, Blanc, Frederic ORCID: 0000-0001-9171-1454, Dyer, Matthew S ORCID: 0000-0002-4923-3003
et al (show 2 more authors) (2022) Cation Disorder and Large Tetragonal Supercell Ordering in the Li-Rich Argyrodite Li7Zn0.5SiS6. CHEMISTRY OF MATERIALS, 34 (9). pp. 4073-4087.

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A tetragonal argyrodite with >7 mobile cations, Li<sub>7</sub>Zn<sub>0.5</sub>SiS<sub>6</sub>, is experimentally realized for the first time through solid state synthesis and exploration of the Li-Zn-Si-S phase diagram. The crystal structure of Li<sub>7</sub>Zn<sub>0.5</sub>SiS<sub>6</sub> was solved <i>ab initio</i> from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li<sub>7</sub>Zn<sub>0.5</sub>SiS<sub>6</sub> adopts a tetragonal <i>I</i>4 structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1 K to a higher symmetry disordered <i>F</i>43<i>m</i> structure more typical of Li-containing argyrodites. Simultaneous occupation of four types of Li site (T5, T5a, T2, T4) at high temperature and five types of Li site (T5, T2, T4, T1, and a new trigonal planar T2a position) at room temperature is observed. This combination of sites forms interconnected Li pathways driven by the incorporation of Zn<sup>2+</sup> into the Li sublattice and enables a range of possible jump processes. Zn<sup>2+</sup> occupies the 48<i>h</i> T5 site in the high-temperature <i>F</i>43<i>m</i> structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in <i>I</i>4 Li<sub>7</sub>Zn<sub>0.5</sub>SiS<sub>6</sub>. The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10<sup>-7</sup> S cm<sup>-1</sup> at room temperature and 4.3(4) × 10<sup>-4</sup> S cm<sup>-1</sup> at 503 K. The transition between the ordered <i>I</i>4 and disordered <i>F</i>43<i>m</i> structures is associated with a dramatic decrease in activation energy to 0.34(1) eV above 411 K. The incorporation of a small amount of Zn<sup>2+</sup> exercises dramatic control of Li order in Li<sub>7</sub>Zn<sub>0.5</sub>SiS<sub>6</sub> yielding a previously unseen distribution of Li sites, expanding our understanding of structure-property relationships in argyrodite materials.

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 19 May 2022 13:59
Last Modified: 18 Jan 2023 21:01
DOI: 10.1021/acs.chemmater.2c00320
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