Direct Observation of Oxide Ion Dynamics in La₂Mo₂O₉ on the Nanosecond Timescale

Abstract

Quasielastic neutron scattering (QENS), underpinned by ab-initio molecular dynamics (AIMD) simulations, has been used to directly observe oxide ion dynamics in solid electrolyte La 2 Mo 2 O 9 on the nanosecond timescale, the longest timescale probed in oxide ion conductors by neutron scattering to date. QENS gives the activation energy of 0.61(5) eV for this process, while AIMD simulations reveal that the exchange processes, which ultimately lead to long-range oxide ion diffusion in La 2 Mo 2 O 9 , rely on the flexibility of the coordination environment around Mo 6+ , with oxide ions jumps occurring between vacant sites both within and between Mo coordination spheres. Simulations also differentiate between the crystallographic sites which participate in the oxide ion exchange processes, offering the first atomic-level understanding of the oxide ion dynamics in La 2 Mo 2 O 9 , which is consistent with the macroscopic experimental observations on this material.

Oxide Ion and Proton Conductivity in Highly Oxygen-Deficient Cubic Perovskite SrSc0.3Zn0.2Ga0.5O2.4

“…This is consistent with impedance measurements, which show that oxide ion conductivity of SSZ40GO at high temperatures (2.9 × 10 –2 S cm –1 at 900 °C) is about 2 orders of magnitude higher than that of undoped SSGO (3 × 10 –4 S cm –1 at 900 °C). These findings are also consistent with our neutron scattering study of La 2 Mo 2 O 9 , which exhibits oxide ion conductivity of 2 × 10 –2 S cm –1 at 600 °C (i.e., the same order of magnitude as SSZ40GO at 900 °C), where QENS signals were observed on IN16B from 570 °C onward …”

“…These findings are also consistent with our neutron scattering study of La 2 Mo 2 O 9 , which exhibits oxide ion conductivity of 2 × 10 −2 S cm −1 at 600 °C (i.e., the same order of magnitude as SSZ40GO at 900 °C), where QENS signals were observed on IN16B from 570 °C onward. 54 Local Structure of SrSc 0.3 Zn 0.2 Ga 0.5 O 2.4 . Powder X-ray and neutron diffraction show that SSZ40GO is a disordered perovskite on average, but from a chemical perspective we expect there to be significant local ordering due to the different coordination preferences of the cations, the large number of oxygen vacancies relative to the ABO 3 perovskite, and the diffuse scattering seen in the NPD pattern.…”

Hexagonal perovskite related oxide ion conductor Ba3NbMoO8.5: phase transition, temperature evolution of the local structure and properties

“…The variable (4, 5, and 6) coordination numbers of Mo 6+ and Nb 5+ have been shown to facilitate high oxide ion conductivity in several mixed metal molybdates and niobates. [27][28][29][30] In Ba 3 NbMoO 8.5 , however, the high oxide ion conductivity was initially linked to the ratio of the number of MO 4 tetrahedra to MO 6 octahedra, 7,8,10,11,31,32 while subsequent average structure determination implied that MO 5 polyhedra are highly likely to be present. 12 The coordination numbers of the M cations in our models were determined using a cut-off of 3.05Å (based on the M-O distance histograms obtained from the RMCProle modelling, Fig.…”

“…34 For example, ve-fold coordination has been reported using a range of different techniques (single crystal and powder X-ray and neutron diffraction, IR and Raman spectroscopy, solid state NMR, computational methods). [27][28][29][30][35][36][37] Oxide ion conductors and other materials with oxide ion mobility are also more likely to exhibit less regular coordination environments. In Ba 3 -NbMoO 8.5 , the ve-fold coordination arises primarily due to the disorder and high level of vacancies in the oxide ion sublattice that are discussed here and in previous reports.…”

Insight into Design of Improved Oxide Ion Conductors: Dynamics and Conduction Mechanisms in the Bi0.913V0.087O1.587 Solid Electrolyte

“…This combined approach has been used to directly observe and elucidate oxide ion dynamics in La 2 Mo 2 O 9 . 16 This study gave the first proof that exchange processes leading to long-range oxide ion diffusion rely on the variability of the coordination number and geometry around the Mo 6+ cations (as postulated in the earlier crystallographic work 17 ), with oxide ions jumps occurring both within and between different Mo coordination spheres. It was also possible to differentiate between the roles of different crystallographic sites, offering the atomic-level understanding of the oxide ion dynamics in La 2 Mo 2 O 9 consistent with the macroscopic experimental observations.…”