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.