Faculty Profiles - SASAKI Takuya

High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P4 Reviewed International journal

Chung-Ching Chang, Takuya Sasaki, Shunsuke Muto, Nico Alexander Gaida, Ken Niwa, Masashi Hasegawa

Journal of Solid State Chemistry Vol. 340 page： 125021 2024.12

High-Pressure Synthesis and Characterization of Novel Inorganic Compounds Invited Reviewed

SASAKI Takuya

The Review of High Pressure Science and Technology Vol. 34 ( 2 ) page： 96 - 102 2024.11

Authorship：Lead author,　Last author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of High Pressure Science and Technology

High-pressure synthesis is a useful method for exploring and synthesizing novel compounds. In this article, transition-metal nitrides and intermetallic compounds of transition-metals and metalloids synthesized under high pressure by utilizing both large-volume press (LVP) and diamond anvil cell (DAC) are reviewed. Further advances in materials science are expected by combining high-pressure synthesis and new reaction process. Control of physical properties by synthetic pressure is achieved in addition to novel compound synthesis.

DOI： 10.4131/jshpreview.34.96

High-Pressure Synthesis of a Novel Molybdenum–Nitrogen Compound and its Anisotropic Axial Compression by Nitrogen Dimers Invited Reviewed Open Access

SASAKI Takuya, ASANO Shuto, NIWA Ken, HASEGAWA Masashi

The Review of High Pressure Science and Technology Vol. 33 ( 4 ) page： 254 - 260 2024.7

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of High Pressure Science and Technology

Pernitrides and polynitrides synthesized under high pressure, containing nitrogen dimers and molecular nitrogen, respectively, are a group of compounds quite different from conventional nitrides synthesized under ambient pressure. Transition-metal polynitrides composed of transition-metal and molecular nitrogen have been synthesized above about 100 GPa, and various types of molecular nitrogen have been discovered. Pernitrides containing nitrogen dimers have anisotropic axial compressibility in the bonding direction of the dimers due to the low compressibility of the dimers. In this article, we review recent progress in molecular nitrogen-containing metal compounds and the anisotropic compression behavior of a novel molybdenum–nitrogen compound, Mo3N5, containing nitrogen dimers.

DOI： 10.4131/jshpreview.33.254

Open Access

Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe3 phase. Reviewed International coauthorship International journal Open Access

Journal of applied crystallography Vol. 57 ( Pt 3 ) page： 755 - 769 2024.6

High-pressure synthesis and low-temperature thermal expansion behavior of homogeneous phosphorus-rich pseudo-binary compound (V0.5Cr0.5)P4 Reviewed International journal

Vol. 49 ( 24 ) page： 40990 - 40994 2023.12

High-Pressure Synthesis of a High-Pressure Phase of MnN Having NiAs-Type Structure. Reviewed International coauthorship International journal

Asano S, Niwa K, Lawler KV, Kawaguchi-Imada S, Sasaki T, Hasegawa M

Inorganic chemistry Vol. 62 ( 49 ) page： 20271 - 20278 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Inorganic Chemistry

A novel high-pressure phase of manganese mononitride, NiAs-type MnN, was successfully synthesized through a pressure-induced phase transition from a tetragonal distorted NaCl-type MnN at pressures above approximately 55 GPa. High-pressure experiments, including starting material preparation, were conducted using a laser-heated diamond anvil cell. This result is the first example of a nitride with a structural phase transition from the distorted NaCl-type to the NiAs-type structure. Upon decompression after the phase transition to NiAs-type structure, the NiAs-type MnN underwent a structural change to the distorted NaCl-type phase, indicating the phase transition was reversible. NiAs-type MnN has a higher density and bulk modulus in comparison to the distorted NaCl-type one. The phase transition pressure of MnN is lower than that of oxides, such as FeO and MnO, which show a structural phase transition from a NaCl-type to a NiAs-type structure. It is suggested that this is due to the lattice distortion caused by antiferromagnetic ordering.

DOI： 10.1021/acs.inorgchem.3c03241

PubMed

Synthesis of garnet-type Mn4+-activated Y3(Al,Ga)5O12 and (Y,Gd)3Al5O12 phosphors with controlled emission by cation substitution Reviewed International journal

Sasaki Takuya, Asaka Ryota, Niwa Ken, Gaida Nico Alexander, Hasegawa Masashi

Journal of the Ceramic Society of Japan Vol. 131 ( 10 ) page： 696 - 700 2023.10

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

Ga- and Gd-substituted garnet-type Y3Al5O12:Mn4+ phosphors, Y3(Al1−xGax)5O12:Mn4+ and (Y1−yGdy)3Al5O12:Mn4+, were synthesized by a conventional solid-state reaction to elucidate the relationship between the emission and the local structure of the activator in the host material. Completely substituted Y3(Al1−xGax)5O12 and ∼80 % substituted (Y1−yGdy)3Al5O12 (y ≤ ∼0.8) solid solutions have been produced. The lattice parameters of the garnet-type solid solutions increased linearly with the substitution of Ga and Gd for Al and Y sites, respectively. The emission peak attributed to the Mn4+ luminescence center of their garnet-type solid solutions shifted toward a longer wavelength side by substituting Ga and Gd. The emission peak wavelength of the Mn4+-activated garnet-type solid solutions increased almost linearly with increasing the average bond length between the cation and anion in the dodecahedral sites. The dodecahedral site in the garnet structure is edge-sharing with the octahedral site where Mn4+ exists. These results indicate that the emission wavelength can be controlled by changing the local structure around Mn4+ due to the cation substitution of coordination polyhedra neighboring Mn4+ coordination polyhedra.

DOI： 10.2109/jcersj2.23063

Thermal expansion behavior of vanadium pernitride, CuAl2-type VN2, synthesized under high pressures Reviewed International journal

Asano S., Niwa K., Sasaki T., Hasegawa M.

Progress in Solid State Chemistry Vol. 72 page： 100426/1 - 100426/5 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Solid State Chemistry

CuAl2-type VN2, which is synthesized under high pressure, is a recoverable material at ambient conditions and has a high bulk modulus. In this study, we investigated the thermal expansion behavior of CuAl2-type VN2 by low-temperature X-ray diffraction measurements between 109.3(5) K and 298.3(8) K. The axial thermal expansion coefficient of VN2 was determined to be αa = 2.7(9) × 10−6 K−1 and αc = 17.8(12) × 10−6 K−1 at 298.3(8) K, which has large anisotropy similar to that of compression behavior. It is found that the small coefficient of thermal expansion of the a-axis is due to the negative and positive effects on the a-axis length with increasing temperature of the bond angles and bond lengths of VN2, respectively. As a result, VN2 exhibits very large anisotropic thermal expansion behavior.

DOI： 10.1016/j.progsolidstchem.2023.100426

Low-temperature thermal expansion behavior of the entropy-stabilized oxide (MgCoNiCuZn)O Reviewed International journal

Materials Letters Vol. 347 ( 15 ) page： 134601/1 - 134601/3 2023.9

High Temperature and Pressure Synthesis, Compression Behaviors and Thermal Expansion of Novel Transition Metal Nitrides Invited Reviewed

Hasegawa Masashi, Asano Shuto, Chang Chung-Ching, Sasaki Takuyta, Niwa Ken

Netsu Sokutei Vol. 50 ( 1 ) page： 13 - 19 2023.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Calorimetry and Thermal Analysis

Pressure is one of the thermodynamic parameters together with the temperature to control the stability of materials. Ultra-high pressure in more than GPa regions allows us to obtain novel transition metal nitrides. This review shows a synthesis system under ultra-high pressures and high temperatures called laser-heating diamond anvil cell system in the first part. Then, our recent research results of the first synthesis of a novel niobium nitride, U2S3-type Nb2N3 are described. In the second part, compression and thermal expansion behaviors of the U2S3-type Nb2N3 are shown and compared with each other. Besides, the high pressure in-situ XRD and low temperature in-situ XRD measurement systems in the Aichi Synchrotron Radiation Center (Aichi SR) are also described briefly.

DOI： 10.11311/jscta.50.1_13

High-pressure synthesis and crystal structures of molybdenum nitride Mo3N5 with anisotropic compressibility by a nitrogen dimer Reviewed International journal

Sasaki T, Yamamoto T, Asano S, Niwa K, Hasegawa M

Dalton transactions Vol. 52 ( 2 ) page： 469 - 475 2023.1

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

A novel high-pressure molybdenum nitride phase, Mo3N5, was synthesized at above 45 GPa via a nitridation reaction of molybdenum with nitrogen under high pressure using a laser-heated diamond anvil cell. Mo3N5, having an N-N dimer and 7-coordinated Mo sites, crystallizes in an orthorhombic structure with a space group of Cmcm (No. 63) without other prototype structures. The refined lattice parameters for Mo3N5 were a = 2.86201(2) Å, b = 7.07401(6) Å, and c = 14.59687(13) Å. The DFT enthalpy calculation suggested that Mo3N5 is a high-pressure stable phase, which is also consistent with an increasing coordination number compared to ambient- and low-pressure phases. The zero-pressure bulk modulus of Mo3N5 was determined to be K0 = 328(4) GPa with K′0 = 10.1(6) by the fitting for the compression curve, which is almost consistent with the theoretical E-V curve and elastic stiffness constants. The compressibility of Mo3N5 has axial anisotropy corresponding to the N-N dimer direction in the crystal structure.

DOI： 10.1039/d2dt03433f

PubMed

Ultra-High-Pressure Synthesis of Transition Metal – Nitrogen Binary Compounds Reviewed Open Access

NIWA Ken, ASANO Shuto, CHANG Chung-Ching, SASAKI Takuya, HASEGAWA Masashi

The Review of High Pressure Science and Technology Vol. 33 ( 1 ) page： 26 - 33 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of High Pressure Science and Technology

The recent development of high-pressure experimental techniques combined with advanced characterization and analytical methods allows us to reveal the crystal chemistry of the transition metal-nitrogen binary compounds up to the megabar pressure regime. Novel early transition metal-nitrogen compounds, VN2, Nb2N3, and MoC-type WN0.6, have been synthesized by using a laser-heated diamond-anvil cell or DIA-type high-pressure apparatus. In addition to conventional high-pressure in-situ X-ray diffraction measurements, the low-temperature thermal expansion behavior and the valance state of transition metal ions of these newly synthesized compounds were revealed. In this article, the details of our experiments, and recent progress in high-pressure synthesis and crystal chemistry of transition metal nitrogen binary compounds are reviewed.

DOI： 10.4131/jshpreview.33.26

Open Access

Crystal Growth of Novel Materials under Ultra-High Pressure and Temperature Reviewed

Hasegawa Masashi, Sasaki Takuya, Gaida Nico A., Niwa Ken

Journal of the Japanese Association for Crystal Growth Vol. 49 ( 2 ) page： n/a 2022.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

Pressure is one of the thermodynamic parameters together with the temperature to control the stability of materials. Ultra-high pressure in GPa ~ Mbar regions allows us to obtain novel materials and crystals. This review shows two crystal growth systems under ultra-high pressure and high temperature are shown in the first part, i.e. multi-anvil large press and laser-heating diamond anvil cell systems. In the second parts, our recent research results of crystal growth by solution growth techniques using these two systems are described including novel incompressible crystals, high aspect-ratio nanowires and rectangular hollow crystals of metal nitrides and oxides.

DOI： 10.19009/jjacg.49-2-02

High-pressure polycrystalline thin-film synthesis and semiconducting property of platinum pernitride Reviewed International journal Open Access

Ken Niwa, Tomoki Iizuka, Masashi Kurosawa, Yuto Nakamura, Hubert Okadome Valencia, Hideo Kishida, Osamu Nakatsuka, Takuya Sasaki, Nico Alexander Gaida, Masashi Hasegawa

AIP Advances Vol. 12 ( 5 ) page： 055318 - 055318 2022.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

A polycrystalline platinum pernitride (PtN2) thin-film was successfully synthesized via nitridation of a platinum thin-film deposited on α-Al2O3 substrate at the pressure of ∼50 GPa by using the laser-heated diamond anvil cell. The current–voltage characteristic and optical reflectance of the synthesized PtN2 thin-film were measured under ambient conditions. Combined with first-principles calculations, these experimental results have revealed that PtN2 exhibits semiconducting property with a bandgap of ∼2 eV. This high-pressure thin-film synthesis technique could also be applied for revealing the physical properties of other novel pernitrides synthesized under ultra-high pressure, which can offer new insights into the physical properties and functionality of the pernitrides and related nitrides.

DOI： 10.1063/5.0090089

Open Access

High pressure synthesis and the valence state of vanadium ions for the novel transition metal pernitride, CuAl2-type VN2 Reviewed International journal

Dalton transactions Vol. 51 ( 7 ) page： 2656 - 2659 2022.2

Reprint of: Automated geometric aberration correction for large-angle illumination STEM Reviewed International journal

Ishikawa, R; Tanaka, R; Morishita, S; Kohno, Y; Sawada, H; Sasaki, T; Ichikawa, M; Hasegawa, M; Shibata, N; Ikuhara, Y

ULTRAMICROSCOPY Vol. 231 page： 113410 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Ultramicroscopy

Depth resolution in scanning transmission electron microscopy (STEM) is physically limited by the illumination angle. In recent notable progress on aberration correction technology, the illumination angle is significantly improved to be larger than 60 milliradians, which is 2 or 3 times larger than those in the previous generation. However, for three-dimensional depth sectioning with the large illumination angles, it is prerequisite to ultimately minimize lower orders of aberrations such as 2- and 3-fold astigmatisms and axial coma. Here, we demonstrate a live aberration correction using atomic-resolution STEM images rather than Ronchigram images. The present method could save the required time for aberration correction, and moreover, it is possible to build up a fully automated program. We demonstrate the method should be useful not only for axial depth sectioning but also phase imaging in STEM including differential phase-contrast imaging.

DOI： 10.1016/j.ultramic.2021.113410