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) A, β=125.302(2)o (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 deg. C whereupon it transforms to a disordered δ-Bi2O3-like phase, which was modeled with δ-Bi2O3 in cubic Fm3-barm with a=5.7809(1) A (Rp=2.49%, wRp=2.44%) at 750 deg. C. Quenching from above 725 deg. 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. - Abstract: 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. Display Omitted