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

Leube, Bernhard, Collins, Chris, Daniels, Luke, Duff, Benjamin, Dang, Yun, Chen, Ruiyong, Gaultois, Michael, Manning, Troy, Blanc, Frederic, Dyer, Matthew, Claridge, John and Rosseinsky, Matthew (2022) Cation Disorder and Large Tetragonal Supercell Ordering in the Li-rich Argyrodite Li7Zn0.5SiS6. [Data Collection]

Description

A tetragonal argyrodite with >7 mobile cations, Li7Zn0.5SiS6, 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 Li7Zn0.5SiS6 was solved ab initio from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li7Zn0.5SiS6 adopts a tetragonal I4 ̅ structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1(5) K to a higher symmetry disordered F4 ̅3m 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 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 Zn2+ into the Li sublattice and enables a range of possible jump processes. Zn2+ occupies the 48h T5 site in the high-temperature F4 ̅3m structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in I4 ̅ Li7Zn0.5SiS6. The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10–7 S cm–1 at room temperature and is 4.3(4) × 10–4 S cm–1at 503 K. The transition between the ordered I4 ̅ and disordered F4 ̅3m 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 Zn2+ exercises dramatic control of Li order in Li7Zn0.5SiS6 yielding a previously unseen distribution of Li sites, expanding our understanding of structure-property relationships in argyrodite materials.

Keywords: Argyrodite, Materials Chemistry, Crystallography, Ionic conductivity
Divisions: Faculty of Science and Engineering > School of Physical Sciences > Chemistry
Depositing User: Luke Daniels
Date Deposited: 24 May 2022 08:03
Last Modified: 24 May 2022 08:03
DOI: 10.17638/datacat.liverpool.ac.uk/1603
URI: https://datacat.liverpool.ac.uk/id/eprint/1603

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