Oxygen Dynamics in Transition Metal-Doped Bismuth Oxides

Abstract

A detailed quasielastic neutron scattering (QENS) study provides direct insights into the mechanism of ionic conduction in the type II transition metal-doped bismuth oxides Bi22W5O48, Bi22Nb5O45.5, and Bi22W2.5Nb2.5O46.75. Quantitative analysis of the QENS broadening reveals an oscillating behavior similar to that observed recently for pure fluorite-type δ-Bi2O3, which can be adequately modeled by a coherent adaption of the Chudley-Elliott jump diffusion model. In conjunction with detailed ab initio molecular dynamics simulations, this shows that oxygen diffuses through these compounds almost exclusively within fluorite-type regions via an isotropic, liquid-like mechanism. The average oxygen jump length is slightly shorter than half the length of the fluorite-type subcell; this is attributed to the flexible coordination environments around Bi, in contrast to the more regular coordination environments around the transition-metal dopants, which localize vacancies and prevent the remaining oxygen atoms from contributing to the overall oxygen diffusivity.

Understanding the Correlation between Oxide Ion Mobility and Site Distributions in Ba3NbWO8.5

“…The structural chemistry of the Ba 3 M 2 O 8.5±δ conductors is complex, and a full understanding of the oxide ion migration pathways and conductivity mechanisms will require good-quality ab initio computational studies of these materials. Although nontrivial due to the complexity and size of the simulation model and the trajectories needed, such computational studies are possible and, especially when interpreted in conjunction with experimental methods, they can provide qualitative and quantitative insight into oxide ion dynamics in structurally complex materials. − …”

“…Although non-trivial due to the complexity and size of the simulation model and the trajectories needed, such computational studies are possible and, especially when interpreted in conjunction with experimental methods, they can provide qualitative and quantitative insight into oxide ion dynamics in structurally complex materials. [30][31][32][33][34][35][36][37]…”

Structure–property correlation in oxide-ion and proton conductors for clean energy applications: recent experimental and computational advancements

“…In the future, this approach may be extended to systems featuring mixed coherent-incoherent scatterers, such as mixed proton-oxide-ion conducting systems. 95,96 For the specic application of proton conducting oxides in SOFCs, one would use a lm (<1 mm) of the proton conductor sandwiched between the electrodes. Differently from powder samples, such lms represent a conned state and, furthermore, can be textured, strained, and exhibit varying degrees of crystallinity, which may affect signicantly the proton conducting properties.…”

“…The experimental work, which we focus on here, has primarily been done by nuclear magnetic resonance (NMR) and QENS and have focused on the determination of conduction pathways, characteristic timescale and activation energies for the ionic motion. 83,[93][94][95][96][97][98] The computational studies, which encompass both static lattice and molecular dynamics techniques, complemented and assisted in the interpretation of experimental data and, therefore, had a predictive role in the improvement of materials.…”

“…These studies thus represent a new, very useful, methodological development for QENS studies of oxide-ion conducting materials. 96 Nevertheless, the indirect information about oxide-ion dynamics by structural probes, such as diffraction methods, is often highly complementary and indispensable for the development of a thorough understanding of the oxide-ion transport in these types of materials. As a very recent example in this regard, we have the combined neutron total scattering and computer simulation study by Marlton et al , on the pyrochlore/defect-fluorite Y 2 Sn 2− x Zr x O 7 , which analyzed the relationship between anion sub-lattice disorder and Frenkel defects facilitating oxide-ion transport.…”