Structure and crystal chemistry of fluorite-related Bi38Mo7O78 from single crystal X-ray diffraction and ab initio calculations

The floating-zone furnace method was used to synthesize single crystals of the fluorite-related δ-Bi2O3-type phase Bi38Mo7O78 for the first time. Single crystal synchrotron X-ray diffraction data, in conjunction with ab initio (density functional theory) calculations, were used to solve, optimize, and refine the 5×3×3 commensurate superstructure of fluorite-type δ-Bi2O3 in Pbcn (a=28.7058(11) Å, b=16.8493(7) Å and c=16.9376(6) Å, Z=4, RF=11.26%, wRI=21.67%). The structure contains stepped channels of Mo6+ in tetrahedral environments along the b axis and chains of Mo6+ in octahedral environments along the ac plane. The role of the stepped channels in oxide ion conduction is discussed. The simultaneous presence of both tetrahedral and octahedral coordination environments for Mo6+, something not previously observed in Mo6+-doped δ-Bi2O3-type phases, is supported by charge balance considerations in addition to the results of crystallographic and ab initio analysis.

The crystal structure of Bi38Mo7O78 with MoO4 and MoO6 represented as polyhedra, Bi atoms as gray spheres, and fluorite-type O atoms as white vertices of Bi–O–Bi bonds.Figure optionsDownload as PowerPoint slide