Structure, crystal chemistry and thermal evolution of the δ-Bi2O3-related phase Bi9ReO17

The thermal evolution and structural properties of fluorite-related δ-Bi2O3-type Bi9ReO17 were studied with variable temperature neutron powder diffraction, synchrotron X-ray powder diffraction and electron diffraction. The thermodynamically stable room-temperature crystal structure is monoclinic P21/c, a=9.89917(5), b=19.70356(10), c=11.61597(6) Å, β=125.302(2)° (Rp=3.51%, wRp=3.60%) and features clusters of ReO4 tetrahedra embedded in a distorted Bi–O fluorite-like network. This phase is stable up to 725 °C whereupon it transforms to a disordered δ-Bi2O3-like phase, which was modeled with δ-Bi2O3 in cubic Fm3¯m with a=5.7809(1) Å (Rp=2.49%, wRp=2.44%) at 750 °C. Quenching from above 725 °C leads to a different phase, the structure of which has not been solved but appears on the basis of spectroscopic evidence to contain both ReO4 tetrahedra and ReO6 octahedra.

The crystal structure of Bi9ReO17 viewed along the [101] direction. Bi atoms and bonds are light gray, O atoms and bonds are black and ReO4 are represented by gray tetrahedra.Figure optionsDownload full-size imageDownload as PowerPoint slide