LiNa2AlF6: a powder structure solution.

Lithium sodium aluminium fluoride was obtained as a white powder by melting a stoichiometric mixture of AlF3, NaF and LiF at 1223 K, and then cooling to 923 K and sintering at this temperature for 4 h. The ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. The monoclinic structure of LiNa2AlF6 can be related to cubic elpasolite. The Li and Al atoms lie on inversion centres. The main octahedral AlF6 structural elements are not deformed, but are rotated slightly with respect to the unit-cell axes. The Li atoms have octahedral coordinations, whereas the Na atoms have cubo-octahedral coordinations. The Na coordination polyhedron is distorted in comparison with that of elpasolite.