Zeta Fe2O3 A new stable polymorph in iron III oxide family


Iron(III) oxide shows a polymorphism, characteristic of the existence of phases with the same chemical composition but distinct crystal structures and, hence, physical properties. Four crystalline phases of iron(III) oxide have previously been identified: α-Fe2O3 (hematite), β-Fe2O3, γ-Fe2O3 (maghemite), and ε-Fe2O3. All four iron(III) oxide phases easily undergo various phase transformations in response to heating or pressure treatment, usually forming hexagonal α-Fe2O3, the most thermodynamically stable Fe2O3 polymorph under ambient conditions. Here, from synchrotron X-ray diffraction experiments, we report the formation of a new iron(III) oxide polymorph that we have termed ζ-Fe2O3 and which evolved during pressure treatment of cubic β-Fe2O3 ( space group) at pressures above 30 GPa. Importantly, ζ-Fe2O3 is maintained after pressure release and represents the first monoclinic Fe2O3 polymorph (I2/a space group) stable at atmospheric pressure and room temperature. ζ-Fe2O3 behaves as an antiferromagnet with a Néel transition temperature of ~69 K. The complex mechanism of pressure-induced transformation of β-Fe2O3, also involving the formation of Rh2O3-II-type Fe2O3 and post-perovskite-Fe2O3 structure, is suggested and discussed concerning a bimodal size distribution of precursor nanoparticles. Due to their different physical properties, which arise from the differences in their crystal structures, all iron(III) oxide polymorphs have found applications in nanotechnology or show considerable promise in such applications. For instance, thin nanocrystalline films of α-Fe2O3 serve as very efficient electrodes in photo-assisted water electrolysis for hydrogen production in solar cells, and α -Fe2O3 nanoparticles are effective catalysts for various heterogeneous catalysis processes. If you are looking for high quality, high purity, and cost-effective Iron Oxide, or if you require the latest price, please email contact mis-asia.

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