Improved oxide-ion and lower proton conduction of hexagonal perovskite-related oxides based on Ba&lt;sub&gt;7&lt;/sub&gt;Nb&lt;sub&gt;4&lt;/sub&gt;MoO&lt;sub&gt;20&lt;/sub&gt; by Cr&lt;sup&gt;6+&lt;/sup&gt; doping

Sakuda, Yuichi; Hester, James; Yashima, Masatomo

doi:10.2109/jcersj2.21192

Cited by 14 publications

(29 citation statements)

References 37 publications

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“…The crystal structures of Ba 7 Nb 4 MoO 20 -based oxides have been extensively investigated. However, all the structural refinements were performed assuming the complete Mo/Nb disorder 11 , 34 – 36 , 38 , 39 , because the Mo 6+ and Nb 5+ cations have both (i) the same number of electrons leading to almost the same X-ray atomic scattering factors and (ii) almost the same neutron scattering lengths (6.715 and 7.054 fm for Mo and Nb, respectively). This indicates a small SCS value for the Mo/Nb pair of 0.037.…”

Section: Introductionmentioning

confidence: 99%

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

et al. 2023

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The chemical order and disorder of solids have a decisive influence on the material properties. There are numerous materials exhibiting chemical order/disorder of atoms with similar X-ray atomic scattering factors and similar neutron scattering lengths. It is difficult to investigate such order/disorder hidden in the data obtained from conventional diffraction methods. Herein, we quantitatively determined the Mo/Nb order in the high ion conductor Ba7Nb4MoO20 by a technique combining resonant X-ray diffraction, solid-state nuclear magnetic resonance (NMR) and first-principle calculations. NMR provided direct evidence that Mo atoms occupy only the M2 site near the intrinsically oxygen-deficient ion-conducting layer. Resonant X-ray diffraction determined the occupancy factors of Mo atoms at the M2 and other sites to be 0.50 and 0.00, respectively. These findings provide a basis for the development of ion conductors. This combined technique would open a new avenue for in-depth investigation of the hidden chemical order/disorder in materials.

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Section: Introductionmentioning

confidence: 99%

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

et al. 2023

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“…[ 31 ] At almost the same time, high oxide‐ion and proton conductivities have been reported for hexagonal perovskite‐related oxides based on Ba 7 Nb 4 MoO 20 that contain intrinsically oxygen‐deficient cubic (c ′ ) layers in their crystal structures. [ 32–37 ] These oxides do not require any chemical substitutions for the high proton conductivity, suggesting that hexagonal perovskite‐related oxides are a promising class of new proton conductors.…”

Section: Introductionmentioning

confidence: 99%

High Proton Conductivity in β‐Ba₂ScAlO₅ Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Murakami

Avdeev

Morikawa

et al. 2022

Adv Funct Materials

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Proton conductors are promising materials for clean energy, but most available materials exhibit sufficient conductivity only when chemically substituted to create oxygen vacancies, which often leads to difficulty in sample preparation and chemical instability. Recently, proton conductors based on hexagonal perovskite‐related oxides have been attracting attention as they exhibit high proton conductivity even without the chemical substitutions. However, their conduction mechanism has been elusive so far. Herein, taking three types of oxides with different stacking patterns of oxygen‐deficient layers (β‐Ba2ScAlO5, α‐Ba2Sc0.83Al1.17O5, and BaAl2O4) as examples, the roles of close‐packed double‐octahedral layers and oxygen‐deficient layers in proton conduction are shown. It is found that “undoped” β‐Ba2ScAlO5, which adopts a structure having alternating double‐octahedral layer and double‐tetrahedral layer with intrinsically oxygen‐deficient hexagonal BaO (h') layer, shows high proton conductivity (≈10−3 S cm−1 above 300 °C), comparable to representative proton conductors. In contrast, the structurally related oxides α‐Ba2Sc0.83Al1.17O5 and BaAl2O4 exhibit lower conductivity. Ab initio molecular dynamics simulations revealed that protons in β‐Ba2ScAlO5 migrate through the double‐octahedral layer, while the h′ layer plays the role of a “proton reservoir” that supplies proton carriers to the proton‐conducting double‐octahedral layers. The distinct roles of the two layers in proton conduction provide a strategy for developing high‐performance proton conductors.

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“…Oxide ions in Ba 7 Nb 4 MoO 20 solid solutions migrate predominantly in the c 0 layers, along 2D diffusional pathways through the lattice tetrahedral and interstitial octahedral oxygen sites as discussed below. 25,157,158 This journal is © The Royal Society of Chemistry 2023 Particularly, the bulk oxide-ion conductivity of Ba 7 Nb 3.9-Mo 1.1 O 20.05 is as high as 5.8 Â 10 À4 S cm À1 at 310 1C, with a low activation energy for oxide-ion conductivity. The interstitial oxygen site, O5, exists in the oxygen-deficient c 0 layer and is essential for the high oxide-ion conductivity.…”

Section: Hexagonal Perovskite Derivativesmentioning

confidence: 99%

“…Substituting the Nb 5+ cation in Ba 7 Nb 4 MoO 20 with an aliovalent cation, such as Mo 6+ , W 6+ , and Cr 6+ can increase its oxide-ion conductivity. 25,157–159 Ba 7 Nb 3.9 Mo 1.1 O 20.05 , 25 Ba 7 Nb 3.85 W 0.15 MoO 20.075 , 157 Ba 7 Nb 3.8 Cr 0.2 MoO 20.1− δ , 158 and Ba 7 Ta 3.7 Mo 1.3 O 20.15 , 159 have greater conductivities than Ba 7 Nb 4 MoO 20 . Particularly, the bulk oxide-ion conductivity of Ba 7 Nb 3.9 Mo 1.1 O 20.05 is as high as 5.8 × 10 −4 S cm −1 at 310 °C, with a low activation energy for oxide-ion conductivity.…”

Section: Introductionmentioning

confidence: 98%

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Recent developments in oxide ion conductors: focusing on Dion–Jacobson phases

Zhang

Yashima

2023

Chem. Commun.

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Improved oxide-ion and lower proton conduction of hexagonal perovskite-related oxides based on Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> by Cr<sup>6+</sup> doping

Cited by 14 publications

References 37 publications

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

High Proton Conductivity in β‐Ba₂ScAlO₅ Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Recent developments in oxide ion conductors: focusing on Dion–Jacobson phases

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Improved oxide-ion and lower proton conduction of hexagonal perovskite-related oxides based on Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> by Cr<sup>6+</sup> doping

Cited by 14 publications

References 37 publications

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

High Proton Conductivity in β‐Ba2ScAlO5 Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers

Recent developments in oxide ion conductors: focusing on Dion–Jacobson phases

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High Proton Conductivity in β‐Ba₂ScAlO₅ Enabled by Octahedral and Intrinsically Oxygen‐Deficient Layers