Cation and anion ordering and clustering in the system Lithian muscovite, Trilithionite and Polylithionite

• Applicants: Privatdozent Dr. Michael Fechtelkord; Dr. Bernd Marler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405948055

The goal of the renewal project is firstly the completion of the syntheses series followed by the standard characterisation with Solid State NMR and XRD. This means to finish the remaining syntheses along the muscovite – trilithionite join and doing selected syntheses along the polylithionite – trilithionite join and the muscovite – trilithionite join with increased hydroxyl and / or fluorine content depending on the results of the two former main series.The second goal is to do sophisticated NMR experiments with the new Bruker AVANCE NEO 400 Solid State NMR Spectrometer including a new additional 2.5 mm FAST MAS NMR probe, which is assumed to operate starting at 07/20, synchrotron diffraction experiments and the acquisition of high-resolution X-ray powder diffraction data with Rietveld crystal structure refinements. Sophisticated NMR experiments involve mainly {19F} and / or {1H} X-CPMAS NMR and HETCOR Spectroscopy (X = 29Si, 27Al, 7Li, 6Li), FAST 19F and 1H MAS NMR with spinning speeds up to 35 kHz, as well as 27Al MQMAS and DQ-SQ NMR experiments. The new digital NMR console facilitates a series of new experiments (ramped CPMAS, MQMAS with z-filter, DQ-SQ NMR, etc.) and because of the digital filtering a much higher resolution compared to the old spectrometer can be achieved. Synchrotron diffraction experiments and the acquisition of high-resolution X-ray powder diffraction (XRD) data with Rietveld crystal structure refinements will give information about the different polytypes present (1M, 2M1, 2M2) and stacking faults in the structure. The presence of the polytypes 1M and 2M1 as derived from the signals in the 19F MAS NMR and FAST MAS NMR spectra has to be verified by XRD experiments. The neighbourhood of [6]Al and [4]Al has to be investigated by {19F} and {1H} 29Si-CPMAS HETCOR and 27Al DQ-SQ NMR spectroscopy. In addition, DFT calculations with the WIEN2K code can give theoretical chemical shift values and electric field gradients for the different polytypes. Compared with the experimental values it will give valuable information about the 19F and 27Al environment.As an additional effect, the results derived from the different investigations will give an insight into phase and field stabilities. So far, very few studies exist on the stability of micas located at the join muscovite – trilithionite - polylithionite.

• DFG Programme: Research Grants