Solid-state chemistry of inorganic fluorides: From tungsten-bronze types to functionalized nanofluorides: A review

Solid-state chemistry of inorganic fluorides has gained great importance in the second half of 20^th century. It aims at identifying the relationships between the structural networks and the physical properties resulting from interactions within these networks. One of the most significant results was the discovery in the 1960s of series of A_xMF₃ fluorides with structures similar to those of tungsten oxide bronzes. The investigation of other compounds mainly based on Al, Ga and transition metals with structures derived from ReO₃, hexagonal tungsten bronze (HTB), tetragonal tungsten bronzes (TTB), defect pyrochlore and perovskite was soon launched in relation, in a first step, to their magnetic properties. Such interest was further extended to various properties such as positive electrodes in Li-ion batteries, UV absorbers, multiferroic components. Today, solid-state inorganic fluorides are present at the nano-sized level as components in many advanced technologies, including Li batteries or all solid-state fluorine batteries, micro- or nano-photonics, up- or down-conversion fluorescent probes, solid-state lasers, nonlinear optics, nuclear cycle, superhydrophobic coatings, etc. It has been pointed out that most of these outstanding properties can be correlated to the exceptional electronic properties of elemental fluorine, F₂.

The aim of this article is to review the solid-state chemistry of fluorides having the formula A_xMF₃ over several decades, from their discovery in the 1960s to the interesting physical-chemical properties more recently investigated on these phases that derive from the ReO₃, perovskite, defect-pyrochlore, hexagonal- and tetragonal- tungsten bronze types.