Host: Japan Association of Mineralogical Sciences
A new high-pressure phase with the composition of Mg2Al2O5 was found. A crystal structure model of the Mg2Al2O5 phase was constructed based on that of ludwigite because the X-ray diffraction pattern of the former is very similar to that of the latter. In the model, (Mg, Al)O6 octahedra connected by edge-sharing and corner-sharing form triangular tunnels in which Mg ions are accommodated. Mg ions in the tunnels have a coordinate environment with trigonal prism-type MgO6. Systematic absences of reflections indicate that the space group of the structure is Pba2 or Pbam. The Rietveld analysis showed that R factor in the case of Pbam was smaller than that in the case of Pba2. This result suggests that the space group of the Ma2Al2O5 phase is Pbam.
