Iron(III) oxide phase with a monoclinic crystal structure


No iron(III) oxide phase with a monoclinic crystal structure stable at atmospheric pressure and room temperature has ever been identified. Thus, ζ-Fe2O3 can be regarded as a new iron(III) oxide polymorphic family member. It is known that the stability of nanoscale Fe2O3 polymorphs is governed by two factors: the Gibbs free energy of the different i-Fe2O3 phases (i = α, β, γ, ε) and the energy barrier associated with the phase transformation. These two parameters, in turn, depend on many factors, such as different phases’ kinetics of formation and (nano)structural properties of the phases’ particles, such as their surface-to-volume ratios. The Gibbs free energy involves the chemical potential and the surface energy. It is generally accepted that surface energy and surface stress/strain are the key properties of nanoparticles that determine the formation and stability of crystalline phases. Because both parameters are strongly related to the nanoparticles’ dimensions, the extent to which a given applied pressure can modify the particles’ crystal structure depends on their size. Therefore, at high pressures, smaller β-Fe2O3 nanoparticles tend to transform into ζ-Fe2O3 while larger β-Fe2O3 nanoparticles primarily transform into α-Fe2O3 and then to perovskite and post-perovskite Fe2O3 phases. We hypothesize that the pressure treatment also affects the chemical potential of ζ-Fe2O3 and that this change (together with changes in the particles’ surface energy) causes the Gibbs free energy of the ζ-Fe2O3 phase to become lower than that of α-Fe2O3 and β-Fe2O3 over a wide range of pressures and temperatures. If you are looking for high quality, high purity, and cost-effective Iron oxide, or if you require the latest price, please feel free to email contact mis-asia.

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