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- Title
Mechanism for the Combined Li–Na Ionic Conductivity in Sugilite (Fe 2 Na 2 K[Li 3 Si 12 O 30 ])-Type Compounds.
- Authors
Park, So-Hyun; Paulmann, Carsten; Hoelzel, Markus; Hochleitner, Rupert
- Abstract
This study explains the ionic conductivity in the mineral sugilite (idealized formula: Fe2Na2K[Li3Si12O30]) by resolving the dynamic disorder of both Li and Na cations using synchrotron X-ray single-crystal diffraction from 298 K to 1023 K. Non-zero anharmonic atomic displacement parameters at Na and Li sites at 1023 K adumbrated long-range charge transport routes for Li and Na cations commonly parallel to the (a–b) plane. Temperature-enhanced diffuse residuals in Fourier maps could unambiguously localize two interstitial sites suitable for Li, as well as three for Na. Each two-dimensional (2D) network of Li and Na interstitials was formed parallel to each other, providing Li and Na hopping pathways. The higher concentration of Na cations hopping in short distances of 2.0962(4)–2.3015(5) Å could be the main reason for the higher bulk conductivity values evaluated by impedance spectra of sugilite in comparison to those of its structural relatives with low Na contents, e.g., the mineral sogdianite ((Zr,Al,Fe)2Na0.36K[Li3Si12O30]). Bond valence sum landscape maps supported the critical role of dynamic disorder of Na+ over densely packed 2D interstitial networks for combined ionic conductivity along with mobile Li+ in sugilite-type compounds.
- Subjects
IONIC conductivity; ATOMIC displacements; VALENCE bonds; X-ray diffraction
- Publication
Minerals (2075-163X), 2023, Vol 13, Issue 5, p620
- ISSN
2075-163X
- Publication type
Article
- DOI
10.3390/min13050620