α-Li3InF6, a ternary fluoride with a new structure type

Abstract

Reaction of anhydrous binary fluorides LiF and InF3 in sealed platinum tube at the temperature gradient 680/670°C yields α-Li3InF6. This low-temperature form crystallizes in the space group P21/m with the cell dimensions a = 4.797(3) A, b = 8.679(1) A, c = 10.366(1) A and β = 90.90(1)°. The framework is built from InF6 and LiF6 octahedra, beside [Li2F6] bitetrahedra. The b-axis seems to be the backbone in the structural features. Running along it, zigzag anionic chains $$({\rm LiF}_4 )_n^{3n - }$$ , resulting from one—edge shared [Li2F10] groups and double files of single InF6 octahedra sharing common corners with [Li2F6], create an approximately hexagonally packed framework in the plane (1 0 0). The antiferroelectric behaviour evident from dielectric studies is confirmed by the antiparallel displacements of In and Li atoms from octahedral centres. This structure is mainly featured by the disorder observed in the lightest atoms. These atoms, which exhibit two kinds of environments, have been refined as two partially occupied sites for the tetrahedral one. Within the Li3MF6 compounds (M: trivalent or 3d element), this new structure reveals unexpected structural features, inducing its ferroic properties.