Work

Ordering of tetrahedral and octahedral layers in synthetic lepidolites and Li-muscovites: two-dimensional { 1 H} → 29 Si ∕ 27 Al CPMAS HETCOR and { 19 F} → 29 Si ∕ 27 Al CPMAS HETCOR spectroscopy

Year: 2025

Type: article

Abstract: Cationic ordering in the octahedral and tetrahedral sheets of synthetic lepidolites with composition K(Li x Al 3− x )[Si 2 x Al 4−2 x O 10 ](OH) y F 2− y and Li-muscovites with K(Li x Al2-x/3□1-2x/3)[Si 3 AlO 10 ](OH) y F 2− y has been investigated using two-dimensional (2-D) {1H/19F}→29Si/27Al cross-polarisation magic-angle-spinning (CPMAS) heteronuclear correlation (HETCOR) solid-state nuclear magnetic resonance (NMR) spectroscopic experiments. The nominal composition ranged between ( x =1.5–2.0; y =0.0–2.0) and ( x =0.0–1.5; y =0.0–2.0), respectively. { 1 H } → 29 Si CPMAS HETCOR solid-state NMR spectra show a clear preferred neighbourhood of the octahedral Li 2 Al-OH environments close to tetrahedral Si(OSi) 3 . On the other hand, the LiAl 2 -OH group shows a preference to be close to Si(OSi) 3 and Si(OAl)(OSi) 2 environments in the tetrahedral sheet. { 19 F } → 29 Si CPMAS HETCOR solid-state NMR spectra show similar results of the Li 2 Al-F environments close to Si(OSi) 3 and LiAl 2 -F groups to be close to the Si(OSi) 3 and Si(OAl)(OSi) 2 environments. However, each 19 F NMR signal is split into two signals. One component of the Li 2 Al-F signal shows a slightly stronger correlation to the Si(OAl) 2 (OSi) groups. Signals resulting from the LiAl 2 -F groups show much lower signal-to-noise ratio, as F prefers to be coordinated by Li 2 Al. { 1 H } → 27 Al 2-D CPMAS HETCOR NMR spectroscopy shows a direct neighbourhood of OH groups to both octahedral and tetrahedral Al but only for OH coordinated by LiAl 2 . For Li 2 Al coordinations, only a correlation to octahedral Al is visible. In the { 19 F } → 27 Al CPMAS HETCOR experiments, the splitting of the Li 2 Al-F signal can be also observed here with a stronger correlation to the [4] Al sites. All results show an ordering of the tetrahedral sheets depending on the octahedral composition. The OH-/F- distribution shows a tendency of an incorporation of F − next to Li-rich environments and of OH − anions next to Al-rich environments.

Source: European Journal of Mineralogy

DOI: 10.5194/ejm-37-877-2025

Authors: Michael Fechtelkord, Lara Sulcek

Institution: Ruhr University Bochum

Language: English

Topic: Clay minerals and soil interactions

Subfield: Biomaterials

Field: Materials Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,024

Funder: Deutsche Forschungsgemeinschaft