Correlation of defect structure and ionic conductivity in δ-phase solid solutions in the Bi3NbO7–Bi3YO6 system

Oxide ion distribution, vacancy ordering and electrical behaviour in the Bi3NbO7–Bi3YbO6pseudo-binary system

“…The occupancy of the 8c site is seen to increase at the expense of the 32f site, with increasing Yb content. This trend is similar to that seen in the Nb/Y analogue 36 and can be associated with the change in the degree of distortion of the average dopant polyhedron, with more distortion of the niobate polyhedra (distorted niobate trigonal anti-prisms in the x = 0.0 composition 23 ), compared to the less distorted ytterbate polyhedra (a distorted octahedral coordination for x = 1.0 34 ). The oxide ion content in the 48i/24d sites does not vary significantly with composition in this system.…”

“…This can be explained by considering that occupancy of these sites is only found in substituted bismuth oxides and is associated with coordination to the substituent cations. 36,37 In the present study, the overall level of bismuth substitution remains the same throughout the studied The thermal variation of the cubic lattice parameter for the studied compositions is shown in is observed with increasing level of Yb content. In order to explain the compositional variation of lattice parameter at elevated temperature, the solid solution mechanism needs to be considered and may be summarised as:…”

“…Samples of general composition 36 For the x = 0.2 composition at room temperature, the position of the 48i site refined to that of the 24d site (0.5, 0.25, 0.25) and in the final refinements was fixed on this site. Crystal and refinement parameters for the data collected at room temperature and at 800°C are given in Tables 1 and 2, respectively.…”

“…The combination of isovalent and aliovalent dopants allows for modification of the vacancy concentration and hence oxide ion conductivity. We have previously examined this effect in the analogous pseudo-binary systems Bi 3 YO 6 -Bi 3 NbO 7 36 and Bi 3 ErO 6 -Bi 3 NbO 7 37 and found compositional, as well as thermal, dependencies of the oxide ion distributions in these systems. In the present study, we examine the compositional and thermal dependence of defect structure and electrical conductivity in the pseudo-binary system Bi 3 YbO 6 -Bi 3 NbO 7 .…”

A 93Nb Solid‐State NMR and Density Functional Theory Study of Four‐ and Six‐Coordinate Niobate Systems

“…[30,101] This is clearly evident in the 93 Nb 3QMAS data of Figure 6; 3QMAS data for a structurally ordered material such as BiNbO 4 produces tightly defined contours and well-defined d iso /C Q results from the inversion process (see Figure 6 a) and b), whereas analogous data for Bi 3 NbO 7 and Sn 2 Nb 2 O 7 yield broad asymmetric resonances and diffuse contours that are consistent with highly disordered systems (see Figure 6 c-f). Less clearly defined solutions for d iso and C Q are delineated by the inversion process for these disordered systems.…”