Crystal structures of the ionic conductors Bi46M8O89 (M = P, V) related to the fluorite-type structure

• Published in: Journal of solid state chemistry Vol. 178; no. 6; pp. 1753 - 1764
• Main Authors: DARRIET, J, LAUNAY, J. C, ZUNIGA, F. J
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier 01-06-2005
• Subjects: Chemical Sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Material chemistry; Materials science; Physics; Ionic conduction; Crystal structures; Oxygen; Space groups; Symmetry property; Vanadium; Ionic conductors; Oxides; Symmetry groups; Lattice parameters; Nonstoichiometry; Fluorite-type superstructure; Monocrystals; Phosphorous; Ambient temperature; Transition elements; Superstructure; Bismuth; X radiation; Fluorite structure; Ionic crystals; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2005.03.013

The crystal structures of the two oxides Bi46M8O89 (M=P, V) have been solved from single crystals X-ray data at room temperature. Bi46P8O89 crystallizes in the monoclinic symmetry (space group C2/m) with the cell parameters a = 19.6073(4) A, b = 11.4181(4) A, c = 21.1119(4) A and β=112.14(3)°. The symmetry of Bi46V8O89 is also monoclinic but the space group is P21/c with the unit-cell parameters: a = 20.0100(4) A, b = 11.6445(4) A, c = 20.4136(4) A and β=107.27(3)°. Both structures derive from an oxygen deficient fluorite-type structure where the Bi and M cations (M=P, V) are ordered in the framework. The structures are characterised by isolated MO4 tetrahedra (M=P, V) which contradicts the previous results. The difference between the two structures is only due to a different order of the M atoms (M=P, V) in the fluorite-type superstructure. It will be shown that some oxygen sites are partially occupied in both structures which can explain the ion conduction properties of these phases. A structural building principle will be proposed that can explain the large domain of solid solution related to the fluorite-type observed in both systems.