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

Yasui, Yuta; Tansho, Masataka; Fujii, Kotaro; Sakuda, Yuichi; Goto, Atsushi; Ohki, Shinobu; Mogami, Yuuki; Iijima, Takahiro; Kobayashi, Shintaro; Kawaguchi, Shogo; Osaka, Keiichi; Ikeda, Kazutaka; Otomo, Toshiya; Yashima, Masatomo

doi:10.1038/s41467-023-37802-4

Cited by 15 publications

(13 citation statements)

References 70 publications

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“…Since the excess oxygen atoms and hydrogen atoms due to the hydration are located in the c ′ layer at 5 K, the water is incorporated forming the O–D (O–H) bonds in the c ′ layer. Thus, the hydration of Ba 7 Nb 3.8 Mo 1.2 O 20.1 occurs in the c ′ layer, which is consistent with the conclusion on Ba 7 Nb 4 MoO 20 · y D 2 O in the literature. , …”

Section: Resultssupporting

confidence: 92%

“…Since Mo and Nb atoms have quite similar neutron scattering lengths, they were assumed to be disordered at each Nb/Mo i cation site ( i = 1, 2, and 3) in the Rietveld and MEM analyses. The oxygen contents w in Ba 7 Nb 3.8 Mo 1.2 O w and Ba 7 Nb 4 MoO w were fixed to be w = 20.1 and 20.0, respectively, in the Rietveld analyses of the neutron-diffraction data taken at 800 °C because TG measurements revealed negligibly small weight changes in dry atmospheres at high temperatures (Figure S16b for Ba 7 Nb 3.8 Mo 1.2 O w and refs , for Ba 7 Nb 4 MoO w ). Refined occupancy factors, low weighted profile reliability factors R wp , and MEM NSLD distributions indicated the presence of interstitial O5 atoms in the c′ layers of both Ba 7 Nb 3.8 Mo 1.2 O 20.1 and Ba 7 Nb 4 MoO 20 at 800 °C (Figures a–d, S17 and Tables S2–S4).…”

Section: Resultsmentioning

confidence: 99%

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Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Sakuda,

Murakami,

Avdeev

et al. 2023

Chem. Mater.

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Oxide-ion and proton conductors have found diverse applications such as in electrolytes of solid-oxide, proton-conducting, and hybrid-ion fuel cells. Research of fuel cells with higher energy efficiency at lower operating temperature has stimulated the search for ion conductors and improved the understanding of the ion-diffusion mechanism. Ion conduction in hexagonal perovskite-related materials is rare, and the mechanism of ion diffusion is unclear. Herein, we report high oxide-ion and proton conductivity (bulk conductivities in wet air: 11 and 2.7 mS cm −1 at 537 and 326 °C, respectively), high chemical, and electrical stability in a new hexagonal perovskite-related oxide Ba 7 Nb 3.8 Mo 1.2 O 20.1 . Total direct current conductivity at 400 °C in wet air of Ba 7 Nb 3.8 Mo 1.2 O 20.1 was 13 times higher than that of Ba 7 Nb 4 MoO 20 . We also report a unique dimer-mediated cooperative mechanism of the high oxide-ion conduction of Ba 7 Nb 3.8 Mo 1.2 O 20.1 (bulk conductivities in dry air: 10 mS cm −1 at 593 °C and 1.1 mS cm −1 at 306 °C). Ab initio molecular dynamics (AIMD) simulations, neutron-diffraction experiments at 800 °C, and neutron scattering length density analyses of Ba 7 Nb 3.8 Mo 1.2 O 20.1 indicated that the excess oxygen atoms are incorporated by the formation of both 5-fold coordinated (Nb/Mo)O 5 monomer and its (Nb/Mo) 2 O 9 dimer with a corner-sharing oxygen atom and that the breaking and reforming of the dimers lead to the high oxide-ion conduction in the oxygen-deficient BaO 2.1 c′ layer. The long distance between Nb/Mo and Ba cations sandwiching the c′ layer of Ba 7 Nb 3.8 Mo 1.2 O 20.1 was found to be responsible for its low activation energy for oxide-ion conduction, leading to high conductivity at low temperatures. AIMD simulations showed that high proton conduction can be attributed to proton migration in the hexagonal close-packed BaO 3 layers of Ba 7 Nb 3.8 Mo 1.2 O 20.1 . The present findings hold a great promise for the development and design of ion conductors.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Sakuda,

Murakami,

Avdeev

et al. 2023

Chem. Mater.

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“…237 237 The Nb/Mo ordering has been recently studied by Yasui et al through the combined use of resonant X-diffraction (which assists for distinguishing atoms with similar X-ray scattering factors and neutron scattering lengths), 95 Mo SS-NMR, and first-principles calculations, concluding that Mo atoms occupy only near the oxygendeficient ion-conducting layer. 238 The amount of extra oxygen was then enlarged by Murakami et al 239 according to Ba 7 Ta 4−x Mo 1+x O 20+x/2 (x = 0.2−0.7). Remarkably, the authors managed to increase the amount of extra oxygen up to Ba 7 Ta 3.7 Mo 1.3 O 20.15 , leading to a higher oxide ion conductivity (1.08 × 10 −3 S•cm −1 at 377 °C) than that observed for Ba 7 Nb 4 MoO 20 .…”

Section: Hexagonal Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

“…Yashima et al further improved the oxide ion conductivity in the Ba 7 Nb 3.9 Mo 1.1 O 20.05 (5.8 × 10 –4 S·cm –1 at 310 °C) by introducing extra oxygen . The Nb/Mo ordering has been recently studied by Yasui et al through the combined use of resonant X-diffraction (which assists for distinguishing atoms with similar X-ray scattering factors and neutron scattering lengths), 95 Mo SS-NMR, and first-principles calculations, concluding that Mo atoms occupy only near the oxygen-deficient ion-conducting layer . The amount of extra oxygen was then enlarged by Murakami et al according to Ba 7 Ta 4– x Mo 1+ x O 20+ x /2 ( x = 0.2–0.7).…”

Section: Hexagonal Perovskite Derivative Oxide Ion Conductorsmentioning

confidence: 99%

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

2023

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This Review presents an overview from the perspective of tetrahedral chemistry on various oxide ion-conducting materials containing tetrahedral moieties which have received continuous growing attention as candidates for key components of various devices, including solid oxide fuel cells and oxygen sensors, due to the deformation and rotation flexibility of tetrahedral units facilitating oxide ion transport. Emphasis is placed on the structural and mechanistic features of various systems ranging from crystalline to amorphous materials, which include a variety of gallates, silicates, germanates, molybdates, tungstates, vanadates, aluminates, niobate, titanates, indium oxides, and the newly reported borates. They contain tetrahedral units in either isolated or linked manners forming different polyhedral dimensionality (0 to 3) with various defect properties and transport mechanisms. The development of oxide ion conductors containing tetrahedral moieties and the elucidation of the roles of tetrahedral units in oxide ion migration have demonstrated diverse opportunities for discovering superior electrolytes for solid oxide fuel cells and other related devices and provided useful clues for uncovering the key factors directing fast oxide ion conduction.

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“…(2) The parent materials Bi 2 R O 4 Cl and Bi 6–2 x Te 2 x O 8+ x Br 2 ( x = 0.5) are the Sillén oxyhalides with the triple fluorite-like layers where the interstitial oxygen sites exist, leading to possible interstitialcy oxide ion diffusion. Recently, the oxide ion conduction via the interstitialcy diffusion has attracted attention due to the high conductivity (e.g., hexagonal perovskite-related oxides, ,− K 2 NiF 4 -type oxides, melilite-type oxides, , scheelite-type oxides, , and mayenite-type oxides). In the present work, Bi 1.9 Te 0.1 LuO 4.05 Cl was found to show high oxide ion conductivity and chemical and electrical stability.…”

Section: Introductionmentioning

confidence: 99%

High Conductivity and Diffusion Mechanism of Oxide Ions in Triple Fluorite-Like Layers of Oxyhalides

Ueno,

Yaguchi,

Fujii

et al. 2024

J. Am. Chem. Soc.

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Oxide ion conductors are attractive materials because of their wide range of applications, such as solid oxide fuel cells. Oxide ion conduction in oxyhalides (compounds containing both oxide ions and halide ions) is rare. In the present work, we found that Sillén oxychlorides, Bi2–x Te x LuO4+x/2Cl (x = 0, 0.1, and 0.2), show high oxide ion conductivity. The bulk conductivity of Bi1.9Te0.1LuO4.05Cl reaches 10–2 S cm–1 at 431 °C, which is much lower than 644 °C of yttria-stabilized zirconia (YSZ) and 534 °C of La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM). Thanks to the low activation energy, Bi1.9Te0.1LuO4.05Cl exhibits a high bulk conductivity of 1.5 × 10–3 S cm–1 even at a low temperature of 310 °C, which is 204 times higher than that of YSZ. The low activation energy is attributed to the interstitialcy oxide ion diffusion in the triple fluorite-like layer, as evidenced by neutron diffraction experiments (Rietveld and neutron scattering length density analyses), bond valence-based energy calculations, static DFT calculations, and ab initio molecular dynamics simulations. The electrical conductivity of Bi1.9Te0.1LuO4.05Cl is almost independent of the oxygen partial pressure from 10–18 to 10–4 atm at 431 °C, indicating the electrolyte domain. Bi1.9Te0.1LuO4.05Cl also exhibits high chemical stability under a CO2 flow and ambient air at 400 °C. The oxide ion conduction due to the two-dimensional interstitialcy diffusion is considered to be common in Sillén oxyhalides with triple fluorite-like layers, such as Bi1.9Te0.1 RO4.05Cl (R = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) and Bi6–2x Te2x O8+x Br2 (x = 0.1, 0.5). The present study opens a new field of materials chemistry: oxide ion-conducting Sillén oxyhalides with triple fluorite-like layers.

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

Cited by 15 publications

References 70 publications

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

High Conductivity and Diffusion Mechanism of Oxide Ions in Triple Fluorite-Like Layers of Oxyhalides

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