Application of an alkoxide sol–gel route for the preparation of complex fluorides of the MAlF4 (M=K,CsM=K,Cs), M3M3AlF6 (M=Li,Na,KM=Li,Na,K), and Na5Al3F14 type

The recently developed sol–gel route for the synthesis of high surface-AlF3 (HS-AlF3) and MgF2 has been extended for alkali fluorides and complex fluorides containing alkali metals and aluminium. The use of component alkoxides in different ratios as precursors gives an easy access to highly distorted materials of the MAlF4 (M=K,CsM=K,Cs), M3M3AlF6 (M=Li,Na,KM=Li,Na,K), and Na5Al3F14 type. In general, the synthesis can be performed at room temperature, within a short time and water-free. A detailed analytical characterization of these compounds is presented including solid state NMR, thermal analysis and X-ray powder diffraction. An attempt to highlight the general ability of a metal to form a gel within this fluoride sol–gel route is made. Possible applications are described and discussed.

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