Masatomo Yashima

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30Years (1997-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

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25 January 2021 in Nature Communications

Journal Article

High oxide-ion conductivity through the interstitial oxygen site in Ba7Nb4MoO20-based hexagonal perovskite related oxides

Masatomo Yashima

Takafumi Tsujiguchi

Yuichi Sakuda

Yuta Yasui

Yu Zhou

Stephen Skinner

Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskite related structures are rare. Herein, we report oxide-ion conductors based on a hexagonal perovskite-related oxide Ba₇Nb₄MoO₂₀. Ba₇Nb_3.9Mo_1.1O_20.05 shows a wide stability range and predominantly oxide-ion conduction in an oxygen partial pressure range from 2 × 10⁻²⁶ to 1 atm at 600 °C. Surprisingly, bulk conductivity of Ba₇Nb_3.9Mo_1.1O_20.05, 5.8 × 10⁻⁴ S cm⁻¹, is remarkably high at 310 °C, and higher than Bi₂O₃- and zirconia-based materials. The high conductivity of Ba₇Nb_3.9Mo_1.1O_20.05 is attributable to the interstitial-O5 oxygen site, providing two-dimensional oxide-ion O1−O5 interstitialcy diffusion through lattice-O1 and interstitial-O5 sites in the oxygen-deficient layer, and low activation energy for oxide-ion conductivity. Present findings demonstrate the ability of hexagonal perovskite related oxides as superior oxide-ion conductors.

3 April 2014 in Chemistry of Materials

Journal Article

New Perovskite-Related Structure Family of Oxide-Ion Conducting Materials NdBaInO₄

Kotaro Fujii

Yuichi Esaki

Kazuki Omoto

Masatomo Yashima

Akinori Hoshikawa

James R. Hester

15 May 2020 in Journal of the American Chemical Society

Journal Article

High Proton Conductivity in Ba₅Er₂Al₂ZrO₁₃, a Hexagonal Perovskite-Related Oxide with Intrinsically Oxygen-Deficient Layers

Taito Murakami

James R. Hester

Masatomo Yashima

8 January 2021 in Nature Communications

Journal Article

Hydride-based antiperovskites with soft anionic sublattices as fast alkali ionic conductors

Shenghan Gao

Thibault Broux

Susumu Fujii

Cédric Tassel

Kentaro Yamamoto

Hiroshi Kageyama

Most solid-state materials are composed of p-block anions, only in recent years the introduction of hydride anions (1s²) in oxides (e.g., SrVO₂H, BaTi(O,H)₃) has allowed the discovery of various interesting properties. Here we exploit the large polarizability of hydride anions (H^–) together with chalcogenide (Ch^2–) anions to construct a family of antiperovskites with soft anionic sublattices. The M₃HCh antiperovskites (M = Li, Na) adopt the ideal cubic structure except orthorhombic Na₃HS, despite the large variation in sizes of M and Ch. This unconventional robustness of cubic phase mainly originates from the large size-flexibility of the H^– anion. Theoretical and experimental studies reveal low migration barriers for Li⁺/Na⁺ transport and high ionic conductivity, possibly promoted by a soft phonon mode associated with the rotational motion of HM₆ octahedra in their cubic forms. Aliovalent substitution to create vacancies has further enhanced ionic conductivities of this series of antiperovskites, resulting in Na_2.9H(Se_0.9I_0.1) achieving a high conductivity of ~1 × 10^–4 S/cm (100 °C).

6 March 2020 in Nature Communications

Journal Article

Oxide-ion conduction in the Dion–Jacobson phase CsBi2Ti2NbO10−δ

Oxide-ion conductors have found applications in various electrochemical devices, such as solid-oxide fuel cells, gas sensors, and separation membranes. Dion–Jacobson phases are known for their rich magnetic and electrical properties; however, there have been no reports on oxide-ion conduction in this family of materials. Here, for the first time to the best of our knowledge, we show the observation of fast oxygen anionic conducting behavior in CsBi₂Ti₂NbO_10−δ. The bulk ionic conductivity of this Dion–Jacobson phase is 8.9 × 10⁻² S cm⁻¹ at 1073 K, a level that is higher than that of the conventional yttria-stabilized zirconia. The oxygen ion transport is attributable to the large anisotropic thermal motions of oxygen atoms, the presence of oxygen vacancies, and the formation of oxide-ion conducting layers in the crystal structure. The present finding of high oxide-ion conductivity in rare-earth-free CsBi₂Ti₂NbO_10−δ suggests the potential of Dion–Jacobson phases as a platform to identify superior oxide-ion conductors.

20 August 2018 in Journal of the American Chemical Society

Journal Article

Chemical Pressure-Induced Anion Order–Disorder Transition in LnHO Enabled by Hydride Size Flexibility

Hiroki Yamashita

Thibault Broux

Yoji Kobayashi

Fumitaka Takeiri

Hiroki Ubukata

Hiroshi Kageyama

About Me

Masatomo Yashima is a Professor at the Department of Chemistry, School of Science, Tokyo Institute of Technology (Tokyo Tech). He received his Ph.D. in 1991 from Tokyo Tech. He has been a principal investigator at Tokyo Tech since April 1997. His group has been studying ceramic materials based on crystal structure analyses. He has successfully performed the crystal structures analyses of ionic conductors, ferroelectric materials, photocatalysts, optical materials, and structural materials. He has also experimentally visualized ion diffusion pathways of ceramic ion conductors using high-temperature neutron diffraction and maximum entropy methods. In recent years, he has focused on the structural design of ceramic ion conductors. His group has been discovering novel, new-structural-type oxide ion conductors and proton conductors exhibiting high conductivities and high chemical and electrical stabilities. He has received more than 77 awards, including the Chemical Society of Japan (CSJ) Award for Creative Work (2018), the Best Teacher Award for Excellence, Tokyo Tech (2014), The American Ceramic Society, Richard and Patricia Spriggs Phase Equilibria Award (2009), the Ceramic Society of Japan (CerSJ) Award for Academic Achievements in Ceramic Science and Technology (2009), the Award of the Crystallographic Society of Japan (2008), Technology Award from Catalyst Manufacturers Association, Japan (2008), and The Japan Institute of Metals and Materials Meritorious Award (2008).

Masatomo Yashima

Masatomo Yashima

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