Faculty Profiles - NIWA, Ken

Papers - NIWA, Ken

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High-Pressure and High-Temperature Synthesis and Crystal Chemistry of Novel Group 14 Element Nitrogen Compounds Invited Reviewed

NIWA Ken, OGASAWARA Hirokazu, YAMANISHI Shogo, SASAKI Takuya, HASEGAWA Masashi

Nihon Kessho Gakkaishi Vol. 66 ( 4 ) page： 230 - 234 2024.12

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

<p>A laser-heated diamond anvil cell（LHDAC）combined with <i>in-situ</i> observation is a very powerful tool for exploring novel materials under high pressure. In this study, silicon, germanium, and tin reacted with nitrogen at pressures above approximately 60 GPa, and pyrite-type pernitrides（<i>A</i>N<sub>2</sub>, <i>A</i>＝Si, Ge, Sn）were synthesized. The zero-pressure bulk moduli of the synthesized pernitrides were found to be systematically higher in the order of SiN<sub>2</sub>, GeN<sub>2</sub>, and SnN<sub>2</sub>. The synthesis process and crystal chemistry of the newly synthesized materials are described.</p>

DOI： 10.5940/jcrsj.66.230

High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P<sub>4</sub> Reviewed

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

JOURNAL OF SOLID STATE CHEMISTRY Vol. 340 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Solid State Chemistry

Pseudo-ternary CrP4-type (V,Cr,Mo)P4 was successfully synthesized at the conditions of 4 GPa and 900 °C by using a large volume multi-anvil-type press. SEM-EDS and STEM analyses revealed that the synthesized pseudo-ternary (V,Cr,Mo)P4 contains almost equimolar amounts of transition metals. The lattice parameters and unit cell volume of (V,Cr,Mo)P4 yield the average value of its end-members. The low-temperature (133 K–333 K) in-situ synchrotron XRD measurements demonstrated that the c-axis showed the highest coefficient of thermal expansion, followed by the b-axis and the a-axis. These thermal behaviors are the same as the binary end-members and pseudo-binary (V,Cr)P4. While from the high-pressure (P < 10 GPa) in-situ synchrotron XRD measurements, it was found that (V,Cr,Mo)P4 showed no phase transition and compression behaviors in which the c-axis was more compressible than the other two axes (b and a) and the b-axis was slightly compressible more than the a-axis. The zero-pressure bulk modulus of 106 (1) GPa and 122.1 (7) GPa were obtained for (V,Cr)P4 and (V,Cr,Mo)P4, respectively. MoP6 octahedral is highly distorted in comparison with VP4 and CrP4, thus the incorporation of MoP4 greatly yields incompressible behaviors of CrP4-type phosphides with respect to temperature and pressure.

DOI： 10.1016/j.jssc.2024.125021

Emergence of New Nitrogen-Rich Compounds in Lead-Nitrogen Phase Diagram Under Pressure Reviewed

Pitié, S; Niwa, K; Frapper, G

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 128 ( 45 ) page： 19410 - 19422 2024.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

In this study, we employed a variable-composition evolutionary algorithm in conjunction with first-principles calculations to perform a comprehensive structural search for the Pb-N binary system under pressure and determine a hyperfine pressure-composition phase diagram. The findings revealed the existence of 11 new pressure-stabilized structures in the pressure range of 0-100 GPa and at 0 K. Six nitrogen-rich compositions, PbNz (z = 2-4, 6, 8, and 10), and seven thermodynamically stable phases were identified. The most prevalent nitrogen motif observed in the predicted PbNz phases is the N2 dumbbell (z = 2-4, 6, and 8). As z increases, the lowest N-N vibrational frequencies decrease from 2076 cm-1 in Im3̅ Pb(N2)4 to 1302 cm-1 in I4/mcm Pb(N2) at 25 GPa. This finding is related to a decrease in the charge transfer from Pb to N2 dimers. The νN-N frequencies act as a clear signature of the existence of high-pressure PbNz phases containing N2 dumbbells. In addition to N2 dimers, the aromatic pentazolate unit N5- is stabilized in the I4/m Pb(cyclo-N5)2 phase, which becomes thermodynamically stable at 25 GPa. This nitrogen-rich phase can be recoverable to ambient pressure and exhibits a high detonation velocity of 10.2 km/s. Additionally, one- and two-dimensional covalent nitrogen nets are also observed in PbNz (z = 6 and 8). Infinite polymeric chains are found in PbN6 and a two-dimensional nitrogen covalent net is encountered in Cc Pb@2D-N8, which is composed of fused aromatic 18-rings.

DOI： 10.1021/acs.jpcc.4c05540

Carbon Nitrides Synthesis using Supercritical Nitrogen Fluid under High-Pressure Reviewed

Niwa Ken, Fukui Riku, Fukai Toshifumi, Alexander Gaida Nico

SPring-8/SACLA Research Report Vol. 12 ( 5 ) page： 303 - 307 2024.10

2-2-2 High-pressure powder X-ray diffraction study of methane-methylcyclopentane hydrate Reviewed

OSAWA Kanta, OGISO Haruto, YONEZAWA Ryohei, SAKATA Masafumi, KIMURA Tomoaki, SASAKI Shigeo, NAGAE Takayuki, NIWA Ken

Proceedings of the Annual Conference of The Japan Institute of Energy Vol. 33 ( 0 ) page： 20 - 21 2024.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Institute of Energy

<p>High-pressure powder X-ray diffraction measurements of methane-methylcyclopentane-water system have been performed in a diamond anvil cell up to 3.1 GPa at room temperature. As a result, a cubic structure II (sII) and a hexagonal structure H (sH) simultaneously form at 0.9 GPa. The sII hydrate which exists up to 2.9 GPa is considered to be composed of methane, methylcyclopentane and water, namely, methane-methylcyclopentane hydrate (MMCPH) because methane or methylcyclopentane with water cannot exist in clathrate hydrate under high pressure. On the other hand, the sH phase possibly comes from methane hydrate. The pressure region of the MMCPH-sII (< 2.9 GPa) is the widest for gas clathrate hydrates ever observed under high pressure at room temperature.</p>

DOI： 10.20550/jietaikaiyoushi.33.0_20

High-pressure X-ray study of NbON oxynitride: direct transition from baddeleyite to cotunnite structure Reviewed

Kozaki, S; Yuan, Y; Ubukata, H; Wei, ZF; Tsumori, T; Asano, S; Niwa, K; Hasegawa, M; Kageyama, H

CHEMISTRY LETTERS Vol. 53 ( 6 ) 2024.6

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

The structural properties of NbON oxynitride under high pressure were investigated through in situ synchrotron X-ray diffraction (SXRD) up to 43 GPa. It was found that the bulk modulus of baddeleyite NbON (290 GPa) is larger than that of ZrO2 (150 GPa), indicating that the introduction of highly covalent nitrogen imparts greater stiffness. Furthermore, SXRD patterns reveal the emergence of a peak signaling a new crystalline phase above around 20 GPa. This is in contrast to TaON, where diffraction patterns only show an increase in background beyond 33 GPa. First-principle calculations suggest that the high-pressure phase adopts an orthorhombic cotunnite-type structure, distinguishing it from the oxide counterparts, wherein the ambient pressure phase transforms to a cotunnite structure via an orthorhombic-I structure.

DOI： 10.1093/chemle/upae113

Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe<sub>3</sub> phase Reviewed Open Access

Voss, L; Gaida, NA; Hansen, AL; Etter, M; Wolff, N; Duppel, V; Lotnyk, A; Bensch, W; Ebert, H; Mankovsky, S; Polesya, S; Bhat, S; Farla, R; Hasegawa, M; Sasaki, T; Niwa, K; Kienle, L

JOURNAL OF APPLIED CRYSTALLOGRAPHY Vol. 57 ( Pt 3 ) page： 755 - 769 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Crystallography

This study reports the synthesis and crystal structure determination of a novel CrTe3 phase using various experimental and theoretical methods. The average stoichiometry and local phase separation of this quenched high-pressure phase were characterized by ex situ synchrotron powder X-ray diffraction and total scattering. Several structural models were obtained using simulated annealing, but all suffered from an imperfect Rietveld refinement, especially at higher diffraction angles. Finally, a novel stoichiometrically correct crystal structure model was proposed on the basis of electron diffraction data and refined against powder diffraction data using the Rietveld method. Scanning electron microscopy-energy-dispersive X-ray spectrometry (EDX) measurements verified the targeted 1:3 (Cr:Te) average stoichiometry for the starting compound and for the quenched high-pressure phase within experimental errors. Scanning transmission electron microscopy (STEM)-EDX was used to examine minute variations of the Cr-to-Te ratio at the nanoscale. Precession electron diffraction (PED) experiments were applied for the nanoscale structure analysis of the quenched high-pressure phase. The proposed monoclinic model from PED experiments provided an improved fit to the X-ray patterns, especially after introducing atomic anisotropic displacement parameters and partial occupancy of Cr atoms. Atomic resolution STEM and simulations were conducted to identify variations in the Cr-atom site-occupancy factor. No significant variations were observed experimentally for several zone axes. The magnetic properties of the novel CrTe3 phase were investigated through temperature- and field-dependent magnetization measurements. In order to understand these properties, auxiliary theoretical investigations have been performed by first-principles electronic structure calculations and Monte Carlo simulations. The obtained results allow the observed magnetization behavior to be interpreted as the consequence of competition between the applied magnetic field and the Cr-Cr exchange interactions, leading to a decrease of the magnetization towards T = 0K typical for antiferromagnetic systems, as well as a field-induced enhanced magnetization around the critical temperature due to the high magnetic susceptibility in this region.

DOI： 10.1107/S1600576724002711

Decompression-Induced In-Plane Lone Pair Electrons in BiSF Synthesized under High Pressure Reviewed

Zhong, CC; Tassel, C; Kato, D; Ogawa, K; Niwa, K; Tomita, O; Ito, Y; Kawaguchi, S; Hasegawa, M; Abe, R; Kageyama, H

CHEMISTRY OF MATERIALS Vol. 36 ( 9 ) page： 4495 - 4501 2024.4

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

Stereochemically active lone pair electrons (LPEs) associated with p-block cations, such as Pb2+ and Bi3+, possess the capability of causing a reduction in the symmetry of crystal structures. However, LPEs leading to steric hindrance may impede structural stabilization; compounds with Bi3+, akin to those containing La3+ with comparable ionic radii, are not always encountered. In this study, we synthesized BiSF using high-pressure (5 GPa) synthesis. BiSF crystallizes in a PbFCl-type structure, exhibiting orthorhombic distortion due to stereochemically active LPEs oriented along the b axis. This contrasts sharply with other PbFCl-type tetragonal compounds (e.g., BiOF), which have van der Waals gaps formed by interlayer LPEs. First-principles calculations and in situ XRD indicate that BiSF is of ideal tetragonal symmetry under high pressure, featuring inactive LPEs. Upon depressurization, a notable expansion of the soft S2- anions occurs, enhancing hybridization between the Bi-6s/6p and S-3s/3p orbitals. This activation of the stereochemistry of LPEs results in a symmetry reduction. BiSF exhibits anisotropic thermal expansion, which is attributed to the contraction of the “LPE-mediated” Bi-F bonds. Our findings illustrate that the direction and shape of LPEs can be tailored during the postsynthesis decompression, underlining high-pressure synthesis as an effective approach for obtaining compounds with stereochemically active LPEs at ambient pressure.

DOI： 10.1021/acs.chemmater.4c00114

High-pressure synthesis of a novel molybdenum–nitrogen compound and its anisotropic axial compression by nitrogen dimers Reviewed

Takuya SASAKI, Shuto ASANO, Ken NIWA, Masashi HASEGAWA

The Review of High Pressure Science and Technology Vol. 33 ( 4 ) 2024

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

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

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

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

A black phosphorus layered homogeneous phosphorus-rich compound – (V0.5Cr0.5)P4 is synthesized using a large volume press under conditions of P = 5 GPa, 1100 °C, and 1 h of heating. (V0.5Cr0.5)P4 has a monoclinic (C2/c) structure with lattice parameters and cell volume of a = 5.2307(3)Å, b = 10.861(4)Å, c = 5.8253(4)Å, β = 110.784°, and V = 309.41(4)Å3, respectively. The thermal expansion behavior above about 110K has been investigated by low-temperature synchrotron XRD. The coefficient of thermal expansion, α, was calculated to be αa = 0.57 × 10−5K−1, αb = 0.70 × 10−5K−1, αc = 0.92 × 10−5K−1, αβ = 0.13 × 10−5K−1 and αv = 2.10 × 10−5K−1 at 293K. This thermal expansion behavior presents an anisotropic expansion characteristic different from pure black phosphorus due to the V/Cr atom that bonded the black phosphorus layers together.

DOI： 10.1016/j.ceramint.2023.09.176

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

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

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

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

PROGRESS IN SOLID STATE CHEMISTRY Vol. 72 page： 100426 - 100426 2023.12

Authorship：Corresponding author 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

新規な14族元素窒化物の超高圧高温合成と結晶化学

丹羽健, 佐々木拓也, 長谷川正

日本結晶学会誌 Vol. 65 ( Supplement ) page： s31 - s31 2023.10

Synthesis of garnet-type Mn<sup>4+</sup>-activated Y<sub>3</sub>(Al,Ga)<sub>5</sub>O<sub>12</sub> and (Y,Gd)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> phosphors with controlled emission by cation substitution Reviewed

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

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

<p>Ga- and Gd-substituted garnet-type Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Mn<sup>4+</sup> phosphors, Y<sub>3</sub>(Al<sub>1−</sub><i><sub>x</sub></i>Ga<i><sub>x</sub></i>)<sub>5</sub>O<sub>12</sub>:Mn<sup>4+</sup> and (Y<sub>1−</sub><i><sub>y</sub></i>Gd<i><sub>y</sub></i>)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Mn<sup>4+</sup>, 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 Y<sub>3</sub>(Al<sub>1−</sub><i><sub>x</sub></i>Ga<i><sub>x</sub></i>)<sub>5</sub>O<sub>12</sub> and ∼80 % substituted (Y<sub>1−</sub><i><sub>y</sub></i>Gd<i><sub>y</sub></i>)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (<i>y</i> ≤ ∼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 Mn<sup>4+</sup> 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 Mn<sup>4+</sup>-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 Mn<sup>4+</sup> exists. These results indicate that the emission wavelength can be controlled by changing the local structure around Mn<sup>4+</sup> due to the cation substitution of coordination polyhedra neighboring Mn<sup>4+</sup> coordination polyhedra.</p>

DOI： 10.2109/jcersj2.23063

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

Chang C.C., Sasaki T., Alexander Gaida N., Niwa K., Hasegawa M.

Materials Letters Vol. 347 2023.9

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

The coefficient of thermal expansion (CTE) of entropy-stabilized oxide (MgCoNiCuZn)O has been firstly experimentally measured and studied at low temperatures below room temperature. The temperature-dependent lattice parameters of (MgCoNiCuZn)O were determined by synchrotron X-ray diffractometry. A CTE value of α = 2.2780x10-5 K−1 at 113 K for (MgCoNiCuZn)O was calculated using a second-degree polynomial fitting. The quenched homogeneous NaCl-type (MgCoNiCuZn)O structure has the highest CTE value below 133 K among all its constituent oxides. An unquenched (MgCoNiCuZn)O was also investigated, and the homogeneity was found to affect CTE values. Finally, the anisotropic behavior of the constituent oxides and (MgCoNiCuZn)O were also compared.

DOI： 10.1016/j.matlet.2023.134601

High Temperature and Pressure Synthesis, Compression Behaviors and Thermal Expansion of Novel Transition Metal Nitrides 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, U<sub>2</sub>S<sub>3</sub>-type Nb<sub>2</sub>N<sub>3</sub> are described. In the second part, compression and thermal expansion behaviors of the U<sub>2</sub>S<sub>3</sub>-type Nb<sub>2</sub>N<sub>3</sub> 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 Mo<sub>3</sub>N<sub>5</sub> with anisotropic compressibility by a nitrogen dimer Reviewed

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

DALTON TRANSACTIONS Vol. 52 ( 2 ) page： 469 - 475 2023.1

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

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

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

SASAKI Takuya, ASANO Shuto, NIWA Ken, HASEGAWA Masashi

The Review of High Pressure Science and Technology Vol. 33 ( 4 ) page： 254 - 260 2023

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

<p>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, Mo<sub>3</sub>N<sub>5</sub>, containing nitrogen dimers.</p>

DOI： 10.4131/jshpreview.33.254

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

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

<p>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, VN<sub>2</sub>, Nb<sub>2</sub>N<sub>3</sub>, and MoC-type WN<sub>0.6</sub>, have been synthesized by using a laser-heated diamond-anvil cell or DIA-type high-pressure apparatus. In addition to conventional high-pressure <i>in-situ</i> 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.</p>

DOI： 10.4131/jshpreview.33.26

High-pressure polycrystalline thin-film synthesis and semiconducting property of platinum pernitride Reviewed 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 (PtN<sub>2</sub>) thin-film was successfully synthesized via nitridation of a platinum thin-film deposited on α-Al<sub>2</sub>O<sub>3</sub> 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 PtN<sub>2</sub> thin-film were measured under ambient conditions. Combined with first-principles calculations, these experimental results have revealed that PtN<sub>2</sub> 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

Synchrotron-Radiation Infrared Microspectroscopy of Marcasite-Type NiN<sub>2</sub> 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

High pressure synthesis and the valence state of vanadium ions for the novel transition metal pernitride, CuAl<sub>2</sub>-type VN<sub>2</sub> 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

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

<p> 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.</p>

DOI： 10.19009/jjacg.49-2-02

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

Crystal and Electronic Structure of U<sub>7</sub>Te<sub>12</sub>-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

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

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

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

<p>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 MN<sub>2</sub>, M<sub>2</sub>N<sub>3</sub>, M<sub>3</sub>N<sub>4</sub>, 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 CrN<sub>2</sub> single crystals, which exhibit the first and only success among novel metal dinitrides.</p>

DOI： 10.11470/oubutsu.89.2_87

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

Lithium ionic conductivities of alpha-LiBO2 with two-dimensional Li-Li networks and gamma-LiBO2 with three-dimensional ones synthesized under high pressure Reviewed

Hirose Eiichi, Kataoka Kunimitsu, Nagata Hiroshi, Akimoto Junji, Sasaki Takuya, Niwa Ken, Hasegawa Masashi

JOURNAL OF SOLID STATE CHEMISTRY Vol. 274 page： 100 - 104 2019.6

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

© 2019 Elsevier Inc. Lithium ionic conductivities of two LiBO 2 polymorphs, i.e. the same composition Li borates: α-LiBO 2 and γ-LiBO 2 , which are ambient and high-pressure phases, have been measured by the AC impedance method between 450 and 520 K using their high-density polycrystalline samples synthesized under high pressures. It is found the intra-grain and total conductivities of the γ-LiBO 2 have been measured for the first time and be of the order 10 −5 ∼ 10 −6 Scm −1 and 10 −6 Scm −1 , respectively, both of which are higher in whole measured temperature range than those of the α-LiBO 2 . The higher lithium ionic conductivities of the former are discussed from the viewpoints of local structure and Li ion network in the crystal structures of the α-LiBO 2 and γ-LiBO 2 .

DOI： 10.1016/j.jssc.2019.02.045

High-pressure synthesis, crystal growth, and compression behavior of hexagonal CrN2 having one-dimensionally aligned nitrogen dimer Reviewed

Niwa Ken, Yamamoto Takurou, Sasaki Takuya, Hasegawa Masashi

PHYSICAL REVIEW MATERIALS Vol. 3 ( 5 ) 2019.5

Infrared spectroscopy on electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and Pt) Reviewed

Soda Kazuo, Komabuchi Mai, Maeguchi Keisuke, Kato Masahiko, Terabe Toshiki, Niwa Ken, Hasegawa Masashi, Ikemoto Yuka, Okamura Hidekazu

PHYSICA B-CONDENSED MATTER Vol. 558 page： 54 - 58 2019.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and N) were investigated via synchrotron radiation infrared spectroscopy and first-principles calculations. Measured reflectance spectra of marcasite-type RuN2 and RhN(2 )showed Drude-like responses, approaching 1 as the photon energy was decreased, whereas reflectance of arsenopyrite-type IrN2 and pyrite-type PtN2 became similar to 0.3 in the low photon energy region with a few features. These findings agreed well with the predictions of the metallic nature of marcasite-type RuN2 and RhN2 and the semiconducting properties of arsenopyrite-type IrN2 and pyrite-type PtN2 , respectively. The measured reflectance spectra were also reasonably consistent with the calculated optical responses. The band gaps of IrN2 and PtN2 were estimated to be 0.8 and 2.1 eV, respectively, via first-principles calculation with a modified Becke-Johnson (MBJ) potential for the exchange potential.

DOI： 10.1016/j.physb.2019.01.017

High-Pressure Synthesis, Crystal Chemistry, and Ionic Conductivity of a Structural Polymorph of Li3BP2O8 Reviewed

Hirose Eiichi, Kataoka Kunimitsu, Nagata Hiroshi, Akimoto Junji, Sasaki Takuya, Niwa Ken, Hasegawa Masashi

INORGANIC CHEMISTRY Vol. 57 ( 24 ) page： 15048 - 15050 2018.12

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

© 2018 American Chemical Society. A new structural polymorph of Li 3 BP 2 O 8 has been successfully synthesized via a solid-state reaction between Li 3 PO 4 and BPO 4 at 4 GPa and 600 °C. The high-pressure phase of Li 3 BP 2 O 8 (HP-Li 3 BP 2 O 8 ) was found to crystallize in monoclinic symmetry with the cell parameters of a = 8.57010(4) Å, b = 11.11812(5) Å, c = 5.55380(3) Å, and β = 97.7269(3)° [space group P2 1 /a (No. 14)]. HP-Li 3 BP 2 O 8 has a new crystal structure that has not been reported so far. The total ionic conductivities measured for the polycrystalline sample by alternating-currrent impedance were 3.4 × 10 -7 and 2.1 × 10 -6 S/cm at 399 and 456 K, respectively. The lithium ionic conductivity of HP-Li 3 BP 2 O 8 was higher than that of the low-pressure phase Li 3 BP 2 O 8 in the temperature range of 375-456 K. This is caused by the difference in the dimensions of the lithium arrangements between LP- and HP-Li 3 BP 2 O 8 .

DOI： 10.1021/acs.inorgchem.8b03155

Structural stability of the Li-ion conductor Li7La3Zr2O12 investigated by high-pressure in-situ X-ray diffraction and Raman spectroscopy

Hirose Eiichi, Niwa Ken, Kataoka Kunimitsu, Akimoto Junji, Hasegawa Masashi

MATERIALS RESEARCH BULLETIN Vol. 107 page： 361 - 365 2018.11

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

© 2018 Elsevier Ltd The high-pressure behavior of Li7La3Zr2O12 (LLZO) with a garnet-related structure has been investigated for the first time by high pressure in situ X-ray diffraction measurements and Raman spectroscopy using a diamond anvil cell. It was found that the tetragonal LLZO transforms to the high-pressure cubic phase (HP-c-LLZO) at 71.8 GPa in a N2 medium and at 25.8 GPa in the absence of pressure mediums. Uniaxial compression in the absence of pressure mediums induced the phase transition at much lower pressures than in the hydrostatic case when N2 was used as the pressure medium. High pressure in situ Raman spectroscopy suggested that the Li coordination in HP-c-LLZO was different from that reported in cubic LLZO, which had been stabilized by doping Al at ambient pressure and room temperature.

DOI： 10.1016/j.materresbull.2018.07.034

Valence-band electronic structures of high-pressure-phase PdF2-type platinum-group metal dioxides MO2 (M = Ru, Rh, Ir, and Pt)

Kazuo Soda, Daichi Kobayashi, Tatsuya Mizui, Masahiko Kato, Yuichi Shirako, Ken Niwa, Masashi Hasegawa, Masaki Akaogi, Hiroshi Kojitani, Eiji Ikenaga, Takayuki Muro

Journal of the Physical Society of Japan Vol. 87 ( 4 ) 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Society of Japan

The valence-band electronic structures of high-pressure-phase PdF2-type (HP-PdF2-type) platinum-group metal dioxides MO2 (M = Ru, Rh, Ir, and Pt) were studied by synchrotron radiation photoelectron spectroscopy and first-principles calculations. The obtained photoelectron spectra for HP-PdF2-type RuO2, RhO2, and IrO2 agree well with the calculated valence-band densities of states (DOSs) for these compounds, indicating their metallic properties, whereas the DOS of HP-PdF2-type PtO2 (calculated in the presence and absence of spin–orbit interactions) predicts that this material may be metallic or semimetallic, which is inconsistent with the electric conductivity reported to date and the charging effect observed in current photoelectron measurements. Compared with the calculated results, the valence-band spectrum of PtO2 appears to have shifted toward the high-binding-energy side and reveals a gradual intensity decrease toward the Fermi energy EF, implying a semiconductor-like electronic structure. Spin-dependent calculations predict a ferromagnetic ground state with a magnetization of 0.475 μB per formula unit for HP-PdF2-type RhO2

DOI： 10.7566/JPSJ.87.044701

High pressure in-situ synthesis and physical properties of Cr3C2-Ni cermets International coauthorship

Wenyan Zhai, Yimin Gao, Liang Sun, Yiran Wang, Ken Niwa, Masashi Hasegawa

CERAMICS INTERNATIONAL Vol. 43 ( 18 ) page： 17202 - 17205 2017.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

A novel Cr3C2-Ni cermets were successfully in-situ synthesized with Cr, C and Ni (20 wt%) mixed-powder at 1100 degrees C under 0-6 GPa isostatic pressure using a small-sized cubic-type multi-anvil press apparatus. High purity Cr3C2 phase was generated in the cermets. Comparing with the conventional and reactive sintering, the sintering temperature and the average grain size of Cr3C2 decreased by 200 degrees C and 50%, respectively. The physical properties, normalized lattice parameters and volumes of Cr3C2 20 wt%Ni cermet as a function of pressure had been studied both experimentally and by first-principles calculations for the first time.

DOI： 10.1016/j.ceramint.2017.09.145

Pyrite form of group-14 element pernitrides synthesized at high pressure and high temperature

K. Niwa, H. Ogasawara, M. Hasegawa

DALTON TRANSACTIONS Vol. 46 ( 30 ) page： 9750 - 9754 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The chemical reaction of group-14 elements with molecular nitrogen at pressures above 60 GPa successfully leads to the formation of pyrite-type pernitrides. These new crystalline group-14 elemental pernitrides were found to show a bulk modulus higher than the other known group-14 elemental nitrides. Our results offer significant new progress in the solid-state chemistry of nitrides.

DOI： 10.1039/c7dt01583f

Microbeam Hard X-ray Photoemission Study on Platinum-Group Metal Pernitrides

Kazuo Soda, Tatsuya Mizui, Mai Komabuchi, Masahiko Kato, Toshiki Terabe, Kentaro Suzuki, Ken Niwa, Yuichi Shirako, Masashi Hasegawa, Masaki Akaogi, Hiroshi Kojitani, Eiji Ikenaga

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 86 ( 6 ) page： 64804 - 64804 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

Using microbeam hard X-ray photoelectron spectroscopy, we clarified the valence-band electronic structures and chemical states of platinum-group metal (Ru, Ir, and Pt) pernitrides, which have been synthesized in supercritical nitrogen fluid under extremely high pressures and temperatures. Their nitrogen contents relative to the platinum-group metal are estimated to be 2 from the photoemission intensity, which is consistent with the studies reported to date. The observed valence-band structures agree quite well with theoretically predicted structures for the pyrite-type PtN2, arsenopyrite-type IrN2, and marcasite-type RuN2. The origin of their extremely large bulk moduli is discussed based on the current results of the valence-band structures and core-level chemical shifts.

DOI： 10.7566/JPSJ.86.064804

Highly Coordinated Iron and Cobalt Nitrides Synthesized at High Pressures and High Temperatures

Ken Niwa, Toshiki Terabe, Daiki Kato, Shin Takayama, Masahiko Kato, Kazuo Soda, Masashi Hasegawa

INORGANIC CHEMISTRY Vol. 56 ( 11 ) page： 6410 - 6418 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above approximately 30 GPa using a laser-heated diamond anvil cell. The synthesized novel transition metal nitrides were found to crystallize into the NiAs-type or marcasite-type structure. NiAs-type FeN could be quenched at ambient pressure, although it was gradually converted to the ZnS-type structure after the pressure was released. On the other hand, CoN was recovered with ZnS-type structure through a phase transition from NiAs-type structure at approximately a few gigapascals during decompression. Marcasite-type CoN2 was also synthesized at pressures above approximately 30 GPa. High-pressure in situ X-ray diffraction measurement showed that the zero-pressure bulk modulus of marcasite-type CoN2 is 216(18) GPa, which is comparable to that of RhN2. This indicates that the interatomic distance of the N-N dimer in marcasite-type CoN2 is short because of weak orbital interaction between cobalt and nitrogen atoms, as in RhN2. Surprisingly, a first-principles electronic band calculation suggests that the NiAs-type FeN and CoN and marcasite-type CoN2 exhibit metallic characteristics with magnetic moments of 3.4, 0.6, and 1.2 mu(B), respectively. The ferromagnetic NiAs-type structure originates from the anisotropic arrangement of transition atoms stacked along the: c axis.

DOI： 10.1021/acs.inorgchem.7b00516

Synthesis, crystal structure and phase transition of a Xe-N-2 compound at high pressure: experimental indication of orbital interaction between xenon and nitrogen

K. Niwa, F. Matsuzaki, M. Hasegawa

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 19 ( 1 ) page： 59 - 63 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The van der Waals compound Xe(N-2)(2) with a C15 Laves structure was successfully synthesised at pressures greater than 4.4 GPa. We found that, at 10 GPa, the structure reversibly transforms from a cubic to a tetragonal phase. Further compression results in changes of Xe-N compound, which could result in the enhancement of orbital interactions between the xenon and nitrogen atoms.

DOI： 10.1039/c6cp06552j

High-Pressure Synthesis and Magnetic Behavior of A-Site Columnar-Ordered Double Perovskites, LnMn(Ga0.5Ti0.5)(2)O-6 (Ln = Sm, Gd)

Gen Shimura, Ken Niwa, Yuichi Shirako, Masashi Hasegawa

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY Vol. 2017 ( 4 ) page： 835 - 839 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A-site columnar-ordered double perovskites, LnMn(Ga0.5Ti0.5)(2)O-6 (Ln = Sm, Gd), were successfully synthesized under high pressure and high temperature (6 GPa, 1375 K). From the synchrotron powder X-ray diffraction patterns, all of the diffraction peaks can be indexed by the P4(2)/nmc space group with lattice parameters a, c approximate to 2a(p) (a(p): primitive cubic perovskite lattice) and no ordering of the B-site cations. Rietveld analysis of the synchrotron powder X-ray diffraction patterns and Curie-Weiss fitting of their magnetizations reveal that the ionic formulae of these perovskites are Ln(3+) Mn2+(Ga0.53+Ti0.54+)(2)O-6(2-). SmMn(Ga0.5Ti0.5)(2)O-6 shows canted-antiferromagnetic behavior, whereas GdMn(Ga0.5Ti0.5)(2)O-6 exhibits two different magnetic states at low temperature depending on the applied magnetic field and shows an unusual magnetization curve. These magnetic behaviors originate by decreasing the antiferromagnetic interaction by substituting Ga3+(d(10)) for Ti4+(d(0)) and by decreasing the ferromagnetic interaction between columnar-ordered Ln(3+) and Mn2+.

DOI： 10.1002/ejic.201601392

Microbeam hard X-ray photoelectron and ion-beam analyses of Nb hydrides formed in supercritical water

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

International Symposium on Atomic Level Characterizations for New Materials and Devices ‘17 Proceedings 2017

High pressure stability and ambient metastability of marcasite-type rhodium pernitride Reviewed

K. Niwa, T. Terabe, K. Suzuki, Y. Shirako, M. Hasegawa

Journal of Applied Physics Vol. 119 page： 065901 2016

Multicomponent A-site ordered perovskite BiMn3(Fe0.25Ti0.75)4O12: High-pressure synthesis, crystal chemistry and magnetic behavior Reviewed

G. Shimura, K. Niwa, Y. Shirako, S. Muto, K. Kusaba, M. Hasegawa

Solid State Communications Vol. 234-235 page： 40-44 2016

Molecular routes syntheses of graphite-like C-N compounds with various N/C ratios in high pressure and temperature Reviewed

T. HORIBE, K. KUSABA, K. NIWA, M. HASEGAWA, K. YASUDA, R. ISHIGAMI

Journal of the Ceramic Society of Japan Vol. 124 ( 10 ) page： 1013-1016 2016

High-pressure synthesis and relationship between A-site ordering and local structure of multicomponent perovskites(Ln0.25Mn0.75) (Al0.25Ti0. 75)O3, Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Y Reviewed

G. Shimura, Y. Shirako, K. Niwa, M. Hasegawa

Journal of Solid State Chemistry Vol. 242 page： 55-62 2016

Angle-resolved hard x-ray photoemission study of Nb hydride formation in high-pressure supercritical water Reviewed

Kazuo Soda, Hiroki Kondo, Kanta Yamaguchi, Masahiko Kato, Tatsuhito Shirak, Ken Niwa, Keiji Kusaba, Masashi Hasegawa, Kozina Xeniya, Eiji Ikenaga

Journal of Alloys and Compounds Vol. 643 page： 195-200 2015

Growth of rectangular hollow tube crystals with rutile-type structure in supercritical fluids Reviewed

K. Niwa, H. Ikegaya, T. Taguchi, S. Muto, T. Tokunaga and M. Hasegawa

Journal of Physics: Conference Series (JPCS) Vol. 500 page： 022007 2014

High pressure synthesis of marcasite-type rhodium pernitride Reviewed International coauthorship

K. Niwa, D. Dzivenko, K. Suzuki, R. Riedel, I. Troyan, M. Eremets and M. Hasegawa

Inorganic Chemistry Vol. 53 page： 697-699 2014

Novel material synthesis using laser-heated diamond anvil cell Invited Reviewed

Vol. 24 page： 178-187 2014

Discovery of the last remaining binary platinum group pernitride RuN2 Reviewed

K. Niwa, K. Suzuki, S. Muto, K. Tatsumi, K. Soda, T. Kikegawa and M. Hasegawa

Chemistry-A European Journal Vol. 20 ( 43 ) page： 13885 - 13888 2014

Characterization of Nb Hydrides Synthesized in High-Pressure Supercritical Water by Micro-beam Hard X-ray Photoelectron Spectroscopy Reviewed

K. Soda, H. Kondo, M. Kato, T. Shiraki, K. Niwa, K. Kusaba, M. Hasegawa, E. Ikenaga

Journal of Electron Spectroscopy and Related Phenomena Vol. 186 page： 54-57 2013

Argon Solubility in SiO2 Melt under High Pressures : A New Experimental Result using Laser-Heated Diamond-Anvil Cell Reviewed

K. Niwa, C. Miyakawa, J. Matsuda, T. Yagi

Earth and Planetary Science Letters Vol. 363 page： 1-8 2013

Pressure-induced noble gas insertion into zeolite LTA and its incompressible behaviors at high pressure Reviewed

K. Niwa, T. Tanaka, M. Hasegawa, T. Okada, T. Yagi, K. Kikegawa

MICROPOROUS AND MESOPOROUS MATERIALS Vol. 182 page： 191-197 2013

Effects of Sn2+ Ion Size on Sn Doped SrTiO3 Reviewed

S. Suzuki, A. Honda, K. Suzuki, S. Higai, A. Ando, K. Niwa, M. Hasegawa

Japanese Journal of Applied Physics Vol. 52 page： 09KC04 2013

In-situ observation of shear stress-induced perovskite to post-perovskite phase transition in CaIrO3 and the development of its deformation texture in a diamond-anvil cell up to 30 GPa Reviewed

K. Niwa, N. Miyajima, Y. Seto, K. Ohgushi, H. Gotou, T. Yagi

Physics of the Earth and Planetary Interiors Vol. 194-195 page： 10–17 2012

High pressure induced water penetration into 3-isopropylmalate dehydrogenase Reviewed

T. Nagae, T. Kawamura, L. Chavas, K. Niwa, M. Hasegawa, C. Kato, N. Watanabe

Acta Crystallographica D Vol. 68 page： 300–309 2012

B1-to-B2 Structural Transitions in Rock Salt Intergrowth Structures Reviewed

T. Yamamoto, Y. Kobayashi, T. Okada, T. Yagi, T. Kawakami, C. Tassel, S. Kawasaki, N. Abe, K. Niwa, T. Kikegawa, N. Hirao, M. Takano, H. Kageyama

Inorg. Chem. Vol. 50 page： 11787-11794 2011.10

Growth and optical properties of rectangular hollow tube TiO2 crystals with rutile-type structure Reviewed

K. Niwa, T. Taguchi, T. Tokunaga, M. Hasegawa

Crystal Growth & Design Vol. 11 ( 10 ) page： 4427-4432 2011.8

Compression behaviors of binary skutterudite CoP3 in noble gases up to 40 GPa at room temperature Reviewed

K. Niwa, D. Nomichi, M. Hasegawa, T. Okada, T. Yagi, T. Kikegawa

Inorganic Chemistry Vol. 50 page： 3281–3285 2011.3

超高圧超高温下での超臨界流体を用いた無機化合物の合成と単結晶育成

長谷川正，丹羽健

セラミックス Vol. 46 page： 378-385 2011

ダイアモンドアンビルセルとレーザー加熱を用いた超高圧超高温超臨界流体中での結晶成長

長谷川正，丹羽健

日本結晶成長学会誌 Vol. 38 page： 4-11 2011

Lattice-preferred orientations in post-perovskite-type MgGeO3 formed by transformations from different pre-phases Reviewed

T. Okada, T. Yagia, K. Niwa, T. Kikegawa

Phys. Earth Planet. Int. Vol. 180 ( 3-4 ) page： 195-202 2010.6

Submicron rectangular hollow tube crystals of rutile-type GeO2 Reviewed

K. Niwa, H. Ikegaya, M. Hasegawa, T. Ohsuna, T. Yagi

J. Crystal Growth Vol. 312 ( 10 ) page： 1731-1735 2010.5

Deformation microtextures in CaIrO3 post-perovskite under high stress conditions using a laser-heated diamond anvil cell Reviewed

N Miyajima, K Niwa, F Heidelbach, T Yagi and K Ohgushi

Journal of Physics: Conference Series Vol. 215 page： 012097 2010

Elasticity of CaIrO3 with perovskite and post-perovskite structure Reviewed

K. Niwa, T. Yagi, K. Ohgushi

Phys. Chem. Minerals page： DOI: 10.1007/s00269-010-0378-z 2010

Decomposition of perovskite FeTiO3 into wustite Fe1-xTi0.5xO and orthorhombic FeTi3O7 at high pressure Reviewed

D. Nishio-Hamane, T. Yagi, M. Ohshiro, K. Niwa, T. Okada, Y. Seto

Physical Review B Vol. 82 page： 092103 2010

Combining FIB milling and conventional Argon ion milling techniques to prepare high-quality site-specific TEM samples for quantitative EELS analysis of oxygen in molten iron Reviewed

N. Miyajima, C. Holzapfel, Y. Asahara, L. Dubrovinsky, D.J. Frost, D.C. Rubie, M. Drechsler, K. Niwa, M. Ichihara, T. Yagi

J. Microsc. Vol. 238 ( 3 ) page： 200-209 2009.6

The stability and equation of state for the cotunnite phase of TiO2 up to 70 GPa Reviewed

D. Nishio-Hamane, A. Shimizu, R. Nakahira, K. Niwa, A. Sano-Furukawa, T. Okada, T. Yagi, T. Kikegawa

Phys. Chem. Minerals Vol. 37 ( 3 ) page： 129-136 2009.3

Synthesis of Ln nitrides (Ln = Ce, Pr, Gd, Lu) in high pressure and temperature Reviewed

K. Niwa, M. Hasegawa, T. Yagi

J. Alloys Compd. Vol. 477 page： 493–497 2009

A new high-pressure polymorph of Ti2O3: implication for high-pressure phase transition in sesquioxide Reviewed

D. Nishio-Hamane, M. Katagiri, K. Niwa, A. Sano-Furukawa, T. Okada, T. Yagi

High Pressure Research Vol. 29 page： 379-388 2009

Solubility of Noble Gas in SiO2 Melt under High Pressure Reviewed

Vol. 18 page： 44-54 2008

DACを用いたMgGeO3ポストペロブスカイト相の塑性変形実験と選択配向の観察 Reviewed

岡田卓，八木健彦，丹羽健

高圧力の科学と技術 Vol. 18 page： 244-253 2008

Lattice Preferred Orientation in CaIrO3 Perovskite and Post-Perovskite Formed by the Plastic Deformation Under Pressure Reviewed

K. Niwa, T. Yagi, K. Ohgushi, S. Merkel, N. Miyajima, T. Kikegawa

Phys. Chem. Minerals Vol. 34 page： 679-686 2007

Synthesis of new La nitrides at high pressure and temperature Reviewed

M. Hasegawa, K. Niwa, T. Yagi

Solid State Commun. Vol. 141 page： 267-272 2007

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