Faculty Profiles - NIWA, Ken

Papers - NIWA, Ken

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Synchrotron-Radiation Infrared Microspectroscopy of Marcasite-Type NiN2 Reviewed

Soda, K; Kawada, T; Niwa, K; Hasegawa, M; Ikemoto, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 91 ( 4 ) 2022.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Physical Society of Japan

The electronic structure of the marcasite-type NiN2, newly synthesized under high pressures and high temperatures, was investigated using synchrotron-radiation infrared (IR) microspectroscopy and first-principles calculations based on the density functional theory (DFT). The IR spectrum of the marcasite-type NiN2 showed characteristic low reflectance of the semiconductor with spectral features probably due to defects or lattice vibrations and free carriers. The effective free-carrier concentration in the marcasite-type NiN2 was estimated by fitting a Drude-Lorentz model for the optical response to be 1024-25 m-3, much less than those of normal metals (1028-29 m-3) and comparable to the estimated concentration of the thermally-excited carrier in the conduction band. The DFT predictions could semi-quantitatively explain the experimental findings; at 36 GPa, the marcasite-type NiN2 had a narrow gap between the Ni 3d aσ bands split in the distorted octahedral coordination of N neighbors.

DOI： 10.7566/JPSJ.91.044702

Web of Science

Scopus

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

Asano, S; Niwa, K; Sasaki, T; Gaida, NA; Hasegawa, M

DALTON TRANSACTIONS Vol. 51 ( 7 ) page： 2656 - 2659 2022.2

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

A novel transition metal pernitride, CuAl2-type VN2, has been synthesized at a pressure above 73.3 GPa. The bulk modulus has been determined to be K0 = 347(12) GPa. By hard X-ray absorption spectrum measurements of VN2, the valence state of transition metal ions in pernitrides has been for the first time experimentally reported.

DOI： 10.1039/d1dt04310b

Web of Science

Scopus

PubMed

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

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

CiNii Research

Pressure-Tunable Crystal Structure and Magnetic Transition Temperature of the Nowotny Chimney-Ladder CrGeγ Phase Reviewed

Sasaki, T; Noda, K; Gaida, NA; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY Vol. 60 ( 19 ) page： 14525 - 14529 2021.10

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

A Nowotny chimney-ladder (NCL) chromium germanide (CrGeγ) with varying compositions has been synthesized under high pressure. Crystal structure parameters of the NCL CrGeγ have been calculated by Le Bail refinement based on the superspace group. The refined γof CrGeγ increases with the synthesis pressure, indicating an increasing Ge content. The NCL CrGeγ phases are ferromagnetic at T = 2 K regardless of their composition, and the magnetic transition temperature (TC) increases when the γbecomes higher. It is noteworthy that CrGe1.763 and CrGe1.774 synthesized at P = 10 and 14 GPa have magnetic transition temperatures of T = 295 and 333 K above room temperature, respectively. Surprisingly, the magnetic transition temperature has changed by δTC = 270 K, although the γvalues of the raw material and the sample synthesized at P = 14 GPa differ by only δγ= 0.05, corresponding to an atomic concentration of 0.62 atom %. The synthesis pressure acts as an essential parameter in tuning the composition of the NCL phase. Accordingly, the high-pressure synthesis may significantly control several physical characteristics of NCL phases by utilizing compositional and structural modulation.

DOI： 10.1021/acs.inorgchem.1c01887

Web of Science

Scopus

PubMed

Crystal and Electronic Structure of U7Te12-Type Tungsten Nitride Synthesized under High Pressure Reviewed

Chang, CC; Sasaki, T; Gaida, NA; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY Vol. 60 ( 17 ) page： 13278 - 13283 2021.9

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

Tungsten nitride continues to drive fundamental interests because of its potential as a functional compound, which combines features such as high hardness together with thermal, chemical, and wear resistance. Here, we report a novel tungsten nitride phase synthesized from MoC-type WN0.6 and molecular nitrogen after laser irradiation at P = 70 GPa in a diamond anvil cell. This novel phase is quenchable at ambient pressure and determined to be U7Te12-type tungsten nitride and crystallizes in the hexagonal space group (P6) having lattice parameters of a = 8.2398(3) Å, c = 2.94948(14) Å, and V = 173.423(13) Å3. Tungsten atoms are coordinated to eight and nine nitrogen atoms, higher than previously reported tungsten nitrides. The bulk modulus is determined to be K0 = 312 (5) GPa (K0′ = 4.0 fixed), and DFT calculations predict that U7Te12-type W7N12 has a metallic nature.

DOI： 10.1021/acs.inorgchem.1c01633

Web of Science

Scopus

PubMed

Nitriding synthesis and structural change of phosphorus nitrides at high pressures Reviewed

Niwa, K; Iijima, Y; Ukita, M; Toda, R; Toyoura, K; Sasaki, T; Matsunaga, K; Gaida, NA; Hasegawa, M

JOURNAL OF RAMAN SPECTROSCOPY Vol. 52 ( 5 ) page： 1064 - 1072 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Raman Spectroscopy

The phase stability of γ-P3N5 and the possible formation of new phosphorus nitrides were investigated via high-pressure in situ Raman spectroscopy, X-ray diffraction measurements, and first-principles calculations up to approximately 80 GPa. In this study, γ-P3N5 was synthesized via the direct nitridation of black phosphorus at a pressure approximately above 12 GPa. The Raman spectrum, bulk modulus (K0 = 130.27(43) GPa), and compression behaviors (order of axial compressibility: βc > βa > βb) were experimentally measured for the first time. These experimental results were in good agreement with those of first-principles calculations. Our high-pressure in situ measurements and first-principles calculations revealed that γ-P3N5 persisted up to 80 GPa at room temperature. The compression of γ-P3N5 proceeded with the folding of the layer consisting of the corner- and edge-sharing PN4 and PN5. The present findings indicate that the P–N bonding with a low coordination number (PN4 and PN5) is preferable and stabilized for phosphorus nitride over a wide pressure range. However, laser heating between 67 and 70 GPa in the presence of nitrogen resulted in the formation of new PxNy, which included the possibility of a new high-pressure P3N5 phase. The Raman scattering measurements along with the decompression demonstrated that the local structure of the newly synthesized PxNy metastably persisted at atmospheric pressure. The present experimental and theoretical studies on phosphorus nitrides offer new insights into the high-pressure behaviors of covalent compounds consisting of highly coordinated polyhedra.

DOI： 10.1002/jrs.6079

Web of Science

Scopus

Electronic Structures of Transition-Metal Pernitrides Studied Using X-ray Absorption and Photoelectron Spectroscopy Reviewed

Soda Kazuo, Kato Daiki, Komabuchi Mai, Terabe Toshiki, Takayama Shin, Ibaragi Toshiki, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Takakura Shoichi, Nakatake Masashi

Journal of the Physical Society of Japan Vol. 90 ( 4 ) page： 44710 - 44710 2021.4

Electronic Structures of Transition-Metal Pernitrides Studied Using X-ray Absorption and Photoelectron Spectroscopy Reviewed

Soda Kazuo, Kato Daiki, Komabuchi Mai, Terabe Toshiki, Takayama Shin, Ibaragi Toshiki, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Takakura Shoichi, Nakatake Masashi

Journal of the Physical Society of Japan Vol. 90 ( 4 ) page： 44710 - 44710 2021.4

Phase relations and thermoelasticity of magnesium silicide at high pressure and temperature Reviewed

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

The Journal of Chemical Physics Vol. 154 ( 14 ) page： 144701 2021.4

Crystal and Electronic Structures of MoSi2-Type CrGe2 Synthesized under High Pressure Reviewed

Takuya Sasaki, Kota Kanie, Tatsuya Yokoi, Ken Niwa, Nico Alexander Gaida, Katsuyuki Matsunaga, Masashi Hasegawa

Inorganic Chemistry Vol. 60 ( 3 ) page： 1767 - 1772 2021.2

Elasticity of nanocrystalline kyanite at high pressure and temperature from ultrasonic and synchrotron X-ray techniques Reviewed

Nico A. Gaida, Steeve Gréaux, Yoshio Kono, Hiroaki Ohfuji, Hideharu Kuwahara, Norimasa Nishiyama, Oliver Beermann, Takuya Sasaki, Ken Niwa, Masashi Hasegawa

Journal of the American Ceramic Society Vol. 104 ( 1 ) page： 635 - 644 2021.1

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

Material properties, such as elasticity data at wide-ranging conditions of pressure and temperature, attract increasing attention for material and earth sciences. In particular, polycrystalline ceramics for next-generation photonic applications are nowadays fabricated by advanced syntheses techniques operating under elevated pressures and temperatures. Herein, the elastic properties of a synthetic transparent and reinforced aluminosilicate nanoceramic composed of triclinic kyanite with minor amounts of trigonal α-alumina crystals are investigated using in situ synchrotron X-ray diffraction and ultrasonic techniques at high-pressure (up to 11 GPa) and high-temperature (300-1500 K) conditions. This not only enables the determination of the equation of state (EoS) parameters by applying the pressure-volume-temperature (P-V-T) data to the high-temperature Birch-Murnaghan EoS but also yields the elastic moduli together with their P and T derivatives from the fit of the compressional and shear wave velocities to a finite strain EoS: KS0,300 = 186(2) GPa, K′S0,300 = 7.2(6), (∂KS0,300/∂T)P = −0.023(2) GPa K−1, G0,300 = 125(1) GPa G′0,300 = 2.3(2), (∂G0,300/∂T)P = −0.017(1) GPa K−1. On the basis of our acquired results, we propose to predict the elastic moduli of aluminosilicate ceramics by a linear function of the ratio of AlO6 octahedra and SiO4 tetrahedra within the constituting phases.

DOI： 10.1111/jace.17464

Web of Science

Scopus

Thermal Expansion of Incompressible U2S3-Type Nb(2)N(3 )Synthesized in a Diamond Anvil Cell

Asano Shuto, Niwa Ken, Sasaki Takuya, Gaida Nico Alexander, Hasegawa Masashi

INORGANIC CHEMISTRY Vol. 59 ( 12 ) page： 7915 - 7918 2020.6

Crystal structures and electronic properties of Sn3N4 polymorphs synthesized via high-pressure nitridation of tin

Niwa Ken, Inagaki Tomoya, Ohsuna Tetsu, Liu Zheng, Sasaki Takuya, Gaida Nico Alexander, Hasegawa Masashi

CRYSTENGCOMM Vol. 22 ( 20 ) page： 3531 - 3538 2020.5

Hydrogen Depth-profiles in Nb Hydrides Formed in Supercritical Water Reviewed

Soda Kazuo, Sugiura Shinya, Yamaguchi Kanta, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Suzuki Kohtaku, Ishigami Ryoya, Ikenaga Eiji

e-Journal of Surface Science and Nanotechnology Vol. 18 page： 152-158 2020.4

Nanowire crystals of tantalum nitride grown in ammonium halide fluxes at high pressures

Gaida Nico Alexander, Sasaki Takuya, Liu Zheng, Niwa Ken, Hirozawa Masaki, Ohsuna Tetsu, Hasegawa Masashi

APPLIED PHYSICS LETTERS Vol. 116 ( 12 ) 2020.3

Microstructural effects on hardness and optical transparency of birefringent aluminosilicate nanoceramics Nico Reviewed Open Access

Gaida, Nico A. Nishiyama, Norimasa Beermann, Oliver Schürmann, Ulrich Masuno, Atsunobu Giehl, Christopher Niwa, Ken Hasegawa, Masashi Bha, Shrikant Farla, Robert Kienle, Lorenz

International Journal of Ceramic Engineering & Science Vol. 2 ( 2 ) page： 76 - 82 2020.3

Synthesis of platinum-group-metal dinitrides by direct nitridation under ultra-high pressures Reviewed

HASEGAWA Masashi, NIWA Ken

Oyo Buturi Vol. 89 ( 2 ) page： 87 - 91 2020.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Applied Physics

It was assumed that platinum-group-metals neither react with nitrogen nor form their nitrides at ambient pressure.However, ultra-high-pressure conditions of more than several dozen GPa have recently made it possible to synthesize their dinitrides by a direct nitridation. This short communication reports on new worldwide trends f of novel metal(M) nitride studies, such as MN2, M2N3, M3N4, particularly platinum-group-metal dinitrides, which can be synthesized only under ultra-high-pressures. The first section deals with an ultra-high-pressure synthesis technique using a diamond anvil cell combined with an infra-red-laser heating system. The next section describes their synthesis, phase stability, crystal structure, and physical properties. Other novel transition-metal dinitrides are also introduced briefly, particularly focusing on the growth of CrN2 single crystals, which exhibit the first and only success among novel metal dinitrides.

DOI： 10.11470/oubutsu.89.2_87

CiNii Research

High-Pressure Synthesis and Crystal Structure of MoC-Type Tungsten Nitride by Nitridation with Ammonium Chloride

Sasaki Takuya, Ikoma Takahide, Sago Kazuki, Liu Zheng, Niwa Ken, Ohsuna Tetsu, Hasegawa Masashi

INORGANIC CHEMISTRY Vol. 58 ( 24 ) page： 16379 - 16386 2019.12

Hydrogen-Storing Salt NaCl(H-2) Synthesized at High Pressure and High Temperature Open Access

Matsuoka Takahiro, Muraoka Shu, Ishikawa Takahiro, Niwa Ken, Ohta Kenji, Hirao Naohisa, Kawaguchi Saori Imada, Ohishi Yasuo, Shimizu Katsuya, Sasaki Shigeo

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 123 ( 41 ) page： 25074 - 25080 2019.10

High-Pressure Synthesis and Phase Stability of Nickel Pernitride

Niwa Ken, Fukui Riku, Terabe Toshiki, Kawada Takuya, Kato Daiki, Sasaki Takuya, Soda Kazuo, Hasegawa Masashi

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY Vol. 2019 ( 33 ) page： 3753 - 3757 2019.9

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Papers - NIWA, Ken