Anomalously High Fluorine Mobility in Tysonite-Like LaF 3 :ScF 3 Nanocrystals: NMR Diffusion Data

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Applied Magnetic Resonance

ORIGINAL PAPER

Anomalously High Fluorine Mobility in Tysonite‑Like ­LaF3:ScF3 Nanocrystals: NMR Diffusion Data L. B. Gulina1   · A. F. Privalov2   · M. Weigler2 · I. V. Murin1   · V. Tolstoy1   · M. Vogel2  Received: 28 May 2020 / Revised: 29 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020

Abstract Nanosized ­La0.93Sc0.07F3 superionic conductor with tysonite structure was obtained at the gas–solution interface after interaction of aqueous salt solution with gaseous HF. NMR diffusion studies show that homovalent substitution of L ­ a3+ by S ­ c3+ with a smaller ionic radius leads to around four orders of magnitude faster fluorine diffusion as compared with crystalline L ­ aF3 and faster as in all previously studied nanosized ­LaF3 and heterovalent-doped nanosized L ­ a0.95Sr0.05F2.95. The homovalent doping is a new route to improve the conductivity of tysonite-structured nanomaterials.

1 Introduction Solid electrolytes based on inorganic fluorides become widely used in chemical sensors, voltaic cells, and many other solid-state electrochemical devices [1]. At medium temperatures, the most promising fluorine superionic conductors are the MII F solid solutions with crystal structures of tysonite or fluorite RIII 1−x x 3−x where III II ­R —is the Y, Sc, or another rare-earth element, and ­M —is the alkaline-earth element or Pb. ­LaF3, crystallizing in tysonite structure, is a prospective ion-conducting solid electrolyte due to its inert nature and high F-conductivity. A number of works [2–8] investigated the influence of crystallochemical features of the tysonite matrix on the ionic transport. Non-stoichiometric heterovalent ­La1−xMxF3−x solid solutions (M–Ca, Sr, Ba, Pb; 0