Anionic Ordering and Thermal Properties of FeF3•3H2O

Iron fluoride trihydrate can be used to prepare iron hydroxyfluoride with the hexagonal-tungsten-bronze (HTB) type structure, a potential cathode material for batteries. To understand this phase transformation, a structural description of beta-FeF3 center dot 3H(2)O is first performed by means of DFT calculations and Mossbauer spectroscopy. The structure of this compound consists of infinite chains of [FeF6](n) and [FeF2(H2O)(4)](n). The decomposition of FeF3 center dot 3H(2)O induces a collapse and condensation of these chains, which lead to the stabilization, under specific conditions, of a hydroxyfluoride network FeF3-x(OH)(x) with the HTB structure. The release of H2O and HF was monitored by thermal analysis and physical characterizations during the decomposition of FeF3 center dot 3H(2)O. An average distribution of FeF4(OH)(2) distorted octahedra in HTB-FeF3-x(OH)(x) was obtained subsequent to the thermal hydrolysis/olation of equatorial anionic positions involving F- and H2O. This study provides a clear understanding of the structure and thermal properties of FeF3 center dot 3H(2)O, a material that can potentially bridge the recycling of pickling sludge from the steel industry by preparing battery electrodes.