Oxygen Insertion Reactions within the One-Dimensional Channels of Phases Related to FeSb₂O₄

Abstract

The structure of the mineral schafarzikite, FeSbO, has one-dimensional channels with walls comprising Sb cations; the channels are separated by edge-linked FeO octahedra that form infinite chains parallel to the channels. Although this structure provides interest with respect to the magnetic and electrical properties associated with the chains and the possibility of chemistry that could occur within the channels, materials in this structural class have received very little attention. Here we show, for the first time, that heating selected phases in oxygen-rich atmospheres can result in relatively large oxygen uptakes (up to ∼2% by mass) at low temperatures (ca. 350 °C) while retaining the parent structure. Using a variety of structural and spectroscopic techniques, it is shown that oxygen is inserted into the channels to provide a structure with the potential to show high one-dimensional oxide ion conductivity. This is the first report of oxygen-excess phases derived from this structure. The oxygen insertion is accompanied not only by oxidation of Fe to Fe within the octahedral chains but also Sb to Sb in the channel walls. The formation of a defect cluster comprising one 5-coordinate Sb ion (which is very rare in an oxide environment), two interstitial O ions, and two 4-coordinate Sb ions is suggested and is consistent with all experimental observations. To the best of our knowledge, this is the first example of an oxidation process where the local energetics of the product dictate that simultaneous oxidation of two different cations must occur. This reaction, together with a wide range of cation substitutions that are possible on the transition metal sites, presents opportunities to explore the schafarzikite structure more extensively for a range of catalytic and electrocatalytic applications.

Synthesis and magnetic characterisation of Fe1−xMgxSb2O4 (x = 0.25, 0.50, 0.75) and their oxygen-excess derivatives, Fe1−xMgxSb2O4+y

“…This increase is caused by the enhanced cation repulsions along the chains after oxidation. 20 At 4 K, fitting using a non-magnetic phase shows additional peaks ( Fig. 13(b)), but these are seen to be very different from those observed for the unoxidised material, Fig.…”

“…to that which we recently reported for other schafarzikiterelated materials. 20 Thermogravimetric analysis of samples containing both Fe and Mg under flowing oxygen is shown in Fig. 6.…”

“…13(a). The excess oxygen was located within the channels in sites previously reported 20 Table 8. Reduction in the bond distances can be attributed to the smaller Fe 3+ ionic radius (compared with Fe 2+ ) 24 and the apical bond to O1 undergoes a larger contraction (3.1%) than the equatorial bond to O2 (1.4%).…”

57Fe Mössbauer spectra from fluorinated phases of Fe0.50M0.50(M = Co,Mg)Sb2O4

“…1 The structure of FeSb 2 O 4 : FeO 6 octahedra are shaded with Fe 2+ ions located within the octahedra; O 2− ions are shown as black spheres and Sb 3+ ions are shown as white spheres − x Mg x Sb 2 O 4 , the decrease in magnetic ordering temperature with increasing concentrations of magnesium was associated with non-magnetic Mg 2+ ions weakening the magnetic interactions between Fe 2+ ions [19,20]. We have also demonstrated the capacity of these materials to accommodate additional oxygen within their structures [21].…”

Reversible Electrochemical Intercalation and Deintercalation of Fluoride Ions into Host Lattices with Schafarzikite‐Type Structure

“…[6b, 10,12] The proposed mechanism forf luorination is based on two key principles. [6b] Firstly,t he phase must possess Fe 2 + to act as the redox active centerw hilst the degree of oxidation is limitedt ot he amount of Fe 2 + to be oxidized to Fe 3 + .F urthermore, it has been shownt hat there is ap ropensity for the Sb 3 + ,w hich line the walls of the channel, to also play ap art in the oxidation process depending on the atmosphere and conditions that the materialish eatedi n. [13] This material is of interest because of the mechanism for the inclusiono fe xcessf luoride ions within the channel of the structure( see Figure1). Therefore, it can be consideredt ob ea 1D intercalation material, like olivine-type materials for lithiumion batteries.…”