Iron(III) oxide polymorphs and their manifestations in in-field [sup 57]Fe Mössbauer spectra

Abstract

Iron(III) oxide, especially when synthesized in the form of nanosized objects, attracts a significant attention of the scientific community due to application-promising attributes empowered by its favorable physical, chemical, and biochemical properties it exhibits. The diversity of its physicochemical features stems from the feasibility to tune the size and morphology of iron(III) oxide nanoparticles and ability to coat their surfaces with variety of organic and inorganic substances, functionalizating them for various purposes. Moreover, iron(III) oxide exhibits a polymorphism; each iron(III) oxide polymorph differs in the crystal structure driving its specific physical properties including its magnetic response under external magnetic fields. In this work, we present the zero-field and in-field 57Fe Mössbauer spectra of all four crystalline iron(III) oxide phases, recorded at both room and low temperature. We demonstrate that the exploitation of in-field 57Fe Mössbauer spectroscopy enables to unambiguously distinguish the iron(III) oxide polymorphs particularly in the case when they exist in the nanosized form and in the mixture. In addition, in-field 57Fe Mössbauer spectroscopy brings additional information on structural features and magnetic behaviors of iron(III) oxide polymorphs.