1 research outputs found
Oxygen Insertion Reactions within the One-Dimensional Channels of Phases Related to FeSb<sub>2</sub>O<sub>4</sub>
The
structure of the mineral schafarzikite, FeSb<sub>2</sub>O<sub>4</sub>, has one-dimensional channels with walls comprising Sb<sup>3+</sup> cations; the channels are separated by edge-linked FeO<sub>6</sub> 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<sup>2+</sup> to Fe<sup>3+</sup> within the octahedral
chains but also Sb<sup>3+</sup> to Sb<sup>5+</sup> in the channel
walls. The formation of a defect cluster comprising one 5-coordinate
Sb<sup>5+</sup> ion (which is very rare in an oxide environment),
two interstitial O<sup>2–</sup> ions, and two 4-coordinate
Sb<sup>3+</sup> 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