title: Type II Bi1 - xWxO1.5 + 1.5x: a (3 + 3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide.
abstract: The Type II phase in the Bi1 - xWxO1.5 + 1.5x system is shown to have a (3 + 3)-dimensional modulated δ-Bi2O3-related structure, in which the modulation vector ℇ `locks in' to a commensurate value of 1/3. The structure was refined in a 3 × 3 × 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi1 - xNbxO1.5 + x (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 `tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along 〈110〉F directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.
authors.affiliation: School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Julia
authors.initials: J
authors.lastname: Wind
authors.affiliation: School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Josie E
authors.initials: JE
authors.lastname: Auckett
authors.affiliation: Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Ray L
authors.initials: RL
authors.lastname: Withers
authors.affiliation: The Bragg Institute, Australian Nuclear Science and Technology Organization, New Illawara Road, Lucas Heights, NSW 2234, Australia.
authors.forename: Ross O
authors.initials: RO
authors.lastname: Piltz
authors.affiliation: Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstrasse 20, Dresden D-01069, Germany.
authors.forename: Andrey
authors.initials: A
authors.lastname: Maljuk
authors.affiliation: School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Ling
keywords: (3+3)-dimensional modulation; floating zone crystal growth; incommensurate; oxide ionic conduction; δ-Bi2O3