A Room‐Temperature Verwey‐type Transition in Iron Oxide, Fe₅O₆

Abstract

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe5O6 stoichiometry. Near 275 K, Fe5O6 undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe−Fe chemical bonds. This unique feature highlights Fe5O6 as a promising candidate for the use in innovative applications. We established that the minimal Fe−Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general.

Electronic properties of single-crystalline Fe4O5

“…5 Recent structural investigations revealed the literature to date [28][29][30][31][32] allowed us to design a general model, which can explain the type and temperature of charge-ordering transitions in different mixed-valence iron oxides. 27 A CaFe 3 O 5 -type crystal structure of Fe 4 O 5 (Fig. 1) is similar to those of other iron ferrites.…”

Orthogonal magnetic structures of Fe4O5: representation analysis and DFT calculations

“…We also note that our calculations were carried out for the charge-averaged structure. Since charge ordering decreases the symmetry of the crystal structure, 3,7 it may also affect the ground state magnetic structure. Nevertheless, it can be treated as a perturbation to the magnetic structures studied here and should not affect the orthogonal nature of the spin configurations.…”

“…Since the discovery of novel high-pressure iron oxides, their crystal chemistry and physical properties have been of great interest. 1–15 Based on the common packing motif, these compounds constitute a homologous series n FeO· m Fe 2 O 3 , containing η-Fe 2 O 3 , HP-Fe 3 O 4 , Fe 4 O 5 , Fe 5 O 6 , Fe 5 O 7 , etc . 4 Their crystal structures consist of two main building blocks, namely the slabs of edge-shared Fe–O octahedra separated by arrays of one-dimensional (1D) chains of Fe ions coordinated by a trigonal prism (see Fig.…”

“…Some members of the series are recoverable under ambient conditions allowing a careful investigation of their physical properties. 3 , 7 Interestingly, the majority of these oxides feature iron ions in the mixed-valence state resulting in a sizeable conductivity 3 , 7,11 and intricate charge-ordering transitions at low temperatures, 3 , 7,12 similar to the famous Verwey transition in magnetite Fe 3 O 4 . 16 At high pressures, a site-selective spin transition is expected in these oxides 15 , 8 , 10 that should have a serious effect on the electronic structure.…”

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

“…Alterations in the Fe-Fe distance in the octahedral chains of various iron oxide colloids can also affect the ability of electrons to hop or tunnel between ions, leading to changes in charge ordering that relates to electrical conductivity (Todo et al, 2001;Senn et al, 2012;Ovsyannikov et al, 2016;Hong et al, 2018;Ovsyannikov et al, 2018;Cassidy et al, 2019;Ovsyannikov et al, 2020) (Figure 4C). Similar effects on electronic properties under pressure (causing structural changes) have been reported for Mah, Hem and Foh NPs (Morris and Williams, 1997;Pasternak et al, 1999;Ohta et al, 2010;Ohta et al, 2012) (Figure 4D).…”