A Combined Total Scattering and Simulation Approach to Analyzing Defect Structure in Bi₃YO₆

Abstract

The defect structure and electrical properties of the fast oxide ion-conducting solid electrolyte δ-Bi 3 YO 6 have been studied using a combination of total neutron scattering analysis, energy minimization methods, and AC impedance spectroscopy. Conventional structural analysis using the Rietveld method reveals the oxide ions to be distributed over three crystallographic sites at room temperature, with a small change in this distribution at 800 °C. Analysis of short-range correlations using a total neutron scattering approach yields information on Bi and Y coordination environments. Careful analysis of the angular distribution functions derived from reverse Monte Carlo modeling of the total scattering data reveals physical evidence for a predominance of AE110ae vacancy ordering in this system. This ordering is confirmed as the lowest energy configuration in parallel energy minimization simulations.

Ab-initio molecular dynamics simulation of δ-Bi3YO6

“…Isovalent substitution of Bi 3+ leads to systems with nominally the same vacancy concentration as in the parent δ-Bi 2 O 3 . However, we have shown that the true vacancy concentration in these substituted bismuth oxides is increased with respect to the parent δ-Bi 2 O 3 , through creation of Frenkel defects [9].…”

“…Structure relaxation was carried out for different vacancy ordering configurations using a single unit cell model (10 atoms), with an 8 × 8 × 8 k mesh, while the random vacancy/cation configuration was relaxed using a 2 × 2 × 2 supercell (80 atoms), with a 2 × 2 × 2 k The initial lattice parameters for Bi 3 YO 6 were obtained from the neutron scattering analysis [9] at 1073 K and the atomic starting positions were based on those in the ideal fluorite structure, i.e. Bi and Y on the 4a sites and O on ¾ of the 8c sites in the Fm-3m unit cell.…”

“…Our own studies using Reverse Monte Carlo modelling of total neutron scattering data on a number of substituted bismuth oxide fluorites, including Bi 3 YO 6 [9], Bi 3 Nb 0.5 Y 0.5 O 6.5 [23] and Bi 4 YbO 7.5 [24], have shown a predominance of b110 > vacancy pair ordering, while atomistic simulation in Bi 3 YO 6 [9] predicts b111 > ordering to be least favoured and b100 > and b110 > to have very similar energies. These studies have revealed that systems have between two and three vacancies per fluorite unit cell, significantly higher than in the parent δ-Bi 2 O 3 itself, the additional vacancies formed by Frenkel defects.…”

“…The composition Bi 3 YO 6 shows exceptionally high conductivity and is readily preserved as a cubic δ-Bi 2 O 3 type phase at room temperature [9,25], despite being metastable with respect to a rhombohedral Bi 3 LaO 6 type phase, which it will transform to on prolonged annealing at ca. 600°C [26][27][28].…”

Does the low optical band gap of yellow Bi3YO6 guarantee the photocatalytical activity under visible light illumination?

“…One of them is Bi 3 YO 6 that occurs in the δ-phase even at room temperature [14]. The defect structure, vacancy ordering, and oxygen ion transport in the Bi 3 YO 6 δ-phase were studied using ab initio molecular dynamic, as well as total neutron scattering analysis [15][16][17]. Ionic transport in a material and its defect structure are commonly tested in Bi 3 NbO 7 -Bi 3 YO 6 systems [18,19] and in tungsten-doped Bi 3 YO 6 [20].…”