Zeta-Fe2O3 – A new stable polymorph in iron(III) oxide family

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 at pressures above30 GPa. Importantly, ζ-Fe₂O₃ is maintained after pressure release and represents the first monoclinic Fe₂O₃ polymorph (I2/a space group) that is 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, involving also the formation of Rh₂O₃-II-type Fe₂O₃ and post-perovskite-Fe₂O₃ structure, is suggested and discussed with respect to a bimodal size distribution of precursor nanoparticles.

Jiří Tuček, Libor Machala, Shigeaki Ono, Asuka Namai, Marie Yoshikiyo, Kenta Imoto, Hiroko Tokoro, Shin-ichi Ohkoshi, Radek Zbořil, Zeta-Fe₂O₃ – A new stable polymorph in iron(III) oxide family. Sci. Rep. 2015, 5, 15091.