Stability and range of the type II Bi1−xWxO1.5+1.5x solid solution

• Published in: Solid state ionics Vol. 308; pp. 173 - 180
• Main Authors: Wind, Julia, Kayser, Paula, Zhang, Zhaoming, Radosavljevic Evans, Ivana, Ling, Chris D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2017
• Subjects: Bismuth oxide; Incommensurately modulated structures; Neutron diffraction; Oxide ionic conductors; Solid solution; XANES; Incommensurately modulated structures; Solid solution; Bismuth oxide; Neutron diffraction; XANES; Oxide ionic conductors
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2017.07.015

We have established the stability and range of the cubic type II phase of Bi1−xWxO1.5+1.5x using a combination of X-ray diffraction, neutron diffraction and X-ray absorption spectroscopy. Type II is a high temperature modification that can be obtained by quenching/rapid cooling of samples with compositions between x=0.148 to x=0.185. Slower cooling rates yield the stable low temperature polymorph, the tetragonal type Ib phase (Bi rich samples), and mixtures of type Ib and Aurivillius phase (W-rich samples). Throughout the entire solid solution range, type II exhibits a (3+3) dimensional incommensurate modulation with modulation vectors slightly smaller than 1/3 based on a cubic fluorite type subcell (δ-Bi2O3). The main structural motifs are well-defined tetrahedra of WO6 octahedra in a δ-Bi2O3-matrix, with additional W being incorporated on corners and face centers of the approximate commensurate 3×3×3 supercell in octahedral coordination, confirmed by XANES analysis of the W L3-edge. Impedance measurements reveal oxide ionic conductivities comparable to those of yttria-stabilised zirconia even after a decrease in ionic conductivity of about half an order of magnitude on thermal cycling due to transition to the tetragonal type Ib phase. •Detailed experimental investigation of the range of the type II solid solution•Establishment of phase relations around the type II phase•Analysis of local coordination environments around W6+•Oxide ionic conductivities similar to yttria stabilised zirconia.