High Pressure Phase transition in Mn2O3 to the CaIrO3-type Phase
Abstract
A recent work by Ono et al. (2005) has revealed that hematite (Fe2O3) undergoes a phase transition at 50 GPa and high-temperature from an orthorhombic structure (Rh2O3-II- or perovskite-type) to the CaIrO3-structure, which has recently been proposed as the structure of the post-perovskite phase in MgSiO3. Therefore understanding the phase transitions of sesquioxides can shed some light on the post-perovskite (Mg,Fe)SiO3 structure and transition. We have studied Mn2O3 (bixbyite) at high pressure using synchrotron X-ray diffraction at the GSECARS sector of the APS and X-17C at the NSLS, and Raman spectroscopy at MIT. Our measurements reveal a phase transition initiating at 27 GPa and completing by 36 GPa when it is compressed at 300 K. The X-ray diffraction patterns of the high-pressure phase are consistent with that of the CaIrO3-type structure. A stiffening of the low-pressure phase begins to occur between 10 and 20 GPa just prior to the initiation of the phase transition at 300 K. We have also laser-heated Mn2O3 using a YAG laser to ~2000 K at 7 GPa. The X-ray diffraction patterns after the heating are consistent with that of the CaIrO3-type structure, thereby demonstrating a wide pressure and temperature stability range for the CaIrO3-type phase in Mn2O3. This phase is not quenchable in Mn2O3. Unlike the earlier predictions that Mn2O3 undergoes a phase transition to either the corundum-, Rh2O3-II, or perovskite-type structure at high pressure due to the suppression of the Jahn-Teller effect, Mn2O3 transforms directly to the CaIrO3-type structure. The octahedron in the CaIrO3-type structure has two pairs of edge shared oxygen atoms and one pair of corner shared oxygen atoms, which may be energetically favorable to host the internal distortion of the octahedron resulting from the Jahn-Teller effect in Mn+3. This may also explain remarkable stability of the CaIrO3-type phase in Mn2O3.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMMR23B0050S
- Keywords:
-
- 3919 Equations of state;
- 3924 High-pressure behavior;
- 3934 Optical;
- infrared;
- and Raman spectroscopy;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction