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Boehnisch, David; Seidel, Stefan; Benndorf, Christopher; Jansen, Thomas; Funke, Lena; Hoffmann, Rolf-Dieter; Heletta, Lukas; Stahl, Juliane; Johrendt, Dirk; Eckert, Hellmut; Juestel, Thomas; Poetgen, Rainer (2018): Na3GaF6 - A crystal chemical and solid state NMR spectroscopic study. In: Zeitschrift für Kristallographie-Crystalline Materials, Vol. 233, No. 7: pp. 479-487
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Abstract

Na3GaF6 and Na3GaF6:Mn4+ samples were obtained from NaNO3 and Ga(NO3)(3)center dot 9H(2)O in hydrofluoric acid using K2MnF6 or NaMnO4 as manganese sources. The structure of Na3GaF6 was studied by single crystal X-ray diffraction at 90, 293, 440 and 500 K, confirming the monoclinic cryolite type structure, space group P2(1)/c. The gallium atoms show slightly distorted octahedral coordination by fluorine atoms, similar to the Nal atoms. Coordination number 8 is observed for Na2. Both sodium sites are clearly distinguished by Na-23 MAS-NMR spectroscopy. Above 400 K the spectra reveal distinct chemical exchange effects, signifying sodium ion hopping between these two sites. At the same time static F-19 NMR spectra indicate pronounced motional narrowing effects in this temperature region. The nearly invariant Ga-69 MAS-NMR spectra suggest that any reorientational motion involving the GaF63- ions (if present) occurs with preservation of the center of mass of these octahedra.