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Papers 【 Display / hide 】

• Introduction of Ag ions into 2H-MoTe2via the high-pressure diffusion control method

  Iwasaki S., Jeem M., Nakano A., Fujioka M.

  Dalton Transactions 55 ( 12 ) 4772 - 4779 2026.03

  ISSN  14779226

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  Transition metal dichalcogenides (TMDs) are a major family of compounds for exploring functional materials through intercalation. In this study, the intercalation of Ag ions into 2H-MoTe<inf>2</inf> using the high-pressure diffusion control (HPDC) method was performed. Due to the application of high pressure (HP), 2H-MoTe<inf>2</inf> with a hexagonal lattice exhibited symmetry-lowered (HP-distorted) domains that can be indexed to a triclinic phase. Owing to the HPDC method, Ag ions were homogeneously distributed throughout the sample. This study opened a pathway for promoting ion introduction and achieving functional modulation in systems where intercalation was previously considered difficult, through a mechanism that is distinct from simple structural changes that merely elongate the interlayer space.

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• Compositional tuning in NaxAlB₁₄ via diffusion control

  Hoshino M., Iwasaki S., Hirai S., Ihara Y., Sugahara T., Morito H., Fujioka M.

  Journal of Alloys and Compounds 1039 2025.09

  ISSN  09258388

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  A uniform Na distribution in NaₓAlB₁₄ was achieved using high-pressure diffusion control (HPDC), which promotes Na deintercalation through enhanced diffusion under high pressure, combined with post-annealing. NaₓAlB₁₄ with a non-stoichiometric Na composition is thermodynamically metastable, and conventional solid-state reactions with adjusted starting compositions typically result in the formation of stoichiometric NaAlB₁₄ and side products. While HPDC alone typically leads to concentration gradients, intentionally halting the Na removal process before complete extraction, followed by annealing, enabled a uniform composition across the bulk. This allowed structural and electronic properties to be examined over a wide range of Na concentrations. As Na content decreased, electrical conductivity increased, and the optical band gap narrowed. NMR measurements showed an increase in the density of states at the Fermi level, consistent with DFT calculations predicting boron-related in-gap states. Boron vacancies at specific sites were found to generate deep levels near the band gap center, which can explain experimentally observed optical gap reduction. These results demonstrate that diffusion-controlling methods can be effectively applied to synthesize metastable compounds with tunable compositions in covalent frameworks. Furthermore, they provide a foundation for designing functional boride-based materials with adjustable electronic properties by controlling Na extraction and inducing defect formation.

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• Hydrogen-Assisted Mg Intercalation into 2H-TaS2

  Fujioka M., Zagarzusem K., Iwasaki S., Sharma A., Watanabe K., Nakayama R., Momai M., Yamaguchi Y., Shimada H., Nomura K., Mizutani Y., Sumi H., Tanaka M., Jeem M., Hattori M., Saitoh H., Ozaki T., Nagao M., Nagashima K.

  Journal of the American Chemical Society 146 ( 50 ) 34324 - 34332 2024.12

  ISSN  00027863

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  Intercalation reactions are highly dependent on the electronic and structural relationships between host and guest materials. It is difficult for divalent ions, such as Mg, to undergo intercalation reactions compared with monovalent cations. However, further development of synthetic techniques for controlling divalent ions is strongly demanded to advance applied chemistry and fundamental physics. In this study, the cointercalation of Mg and H into the transition-metal chalcogenide TaS<inf>2</inf> was utilized to obtain bulk polycrystalline Mg<inf>x</inf>H<inf>y</inf>TaS<inf>2</inf>. Introduced H can be extracted via postannealing at approximately 400 °C without altering the crystal structure. This study clarified the relationship between superconducting properties and electronic carrier density from the perspectives of calculations and experiments, along with the advantages of using hydride as a multivalent intercalation reaction.

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• Effect of intergranular connectivity of NaAlB14 on Na+ extraction

  Iwasaki S., Hoshino M., Morito H., Kumagai M., Katsura Y., Nishii J., Fujioka M.

  Solid State Sciences 144 2023.10

  ISSN  12932558

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  This study investigated the effect of intergranular connectivity when Na⁺ was extracted from polycrystalline NaAlB<inf>14</inf> to the Y-type zeolite via anisotropic ion diffusion control (ADC) and high-pressure diffusion control (HPDC) methods. Despite the low chemical intergranular connectivity in NaAlB<inf>14</inf> without pre-annealing, Na⁺ was homogeneously extracted via HPDC process. Although the HPDC can form a strong physical compression between particles, the intergranular domain of the sample was oxidized by the backflow of oxide ions from the zeolite. Such oxidization can be solved by pre-annealing for chemical intergranular connectivity. In the case of Na⁺ extraction via ADC process, Na⁺ remained at the cathode side even after the treatment for 230 h. From the comparison between ADC and HPDC processes, a strong physical compression between particles by applying pressure can promote the diffusion of Na⁺. Therefore, pre-annealing and high-pressure applications are essential for ion diffusion control techniques.

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• 93 at.% of Na extraction from a Na24Si136 single crystal via anisotropic ion diffusion control method

  Iwasaki S., Morito H., Hoshino M., Nishii J., Fujioka M.

  Journal of Solid State Chemistry 324 2023.08

  ISSN  00224596

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  An allotrope of Si, Si<inf>136</inf>, is a promising semiconductor for photovoltaics due to its direct bandgap. Si<inf>136</inf> is synthesized via Na extraction from Na<inf>24</inf>Si<inf>136</inf>. In this study, 93 at.% of Na extraction from a single crystal of Na<inf>24</inf>Si<inf>136</inf> was achieved using high-pressure-annealed zeolite as an ion absorber. The residual amount of Na is the least record among Na extraction from a single-crystalline Na<inf>24</inf>Si<inf>136</inf>. Na diffusion between the grains of amorphous phases of zeolite was suggested to be improved due to high-pressure annealing.

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