研究者詳細 - 佐々木　拓也

論文 - 佐々木　拓也

分割表示 43 件中 1 - 20 件目／全件表示 >>

Pressure-Tunable Crystal Structure and Magnetic Transition Temperature of the Nowotny Chimney-Ladder CrGeγ Phase 査読有り国際誌

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

INORGANIC CHEMISTRY 60 巻 ( 19 ) 頁： 14525 - 14529 2021年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 Structures of MoSi2-Type CrGe2 Synthesized under High Pressure. 査読有り国際誌

Sasaki T, Kanie K, Yokoi T, Niwa K, Gaida NA, Matsunaga K, Hasegawa M

Inorganic Chemistry 60 巻 ( 3 ) 頁： 1767 - 1772 2021年1月

High-pressure synthesis via glass and photoluminescence properties of BaGe2O5 III-type SrSi2O5:Eu2+ with 12-coordinated Sr2+ site 査読有り Open Access

Kitahara T., Sasaki T., Saito G., Niwa K., Hasegawa M.

Ceramics International 51 巻 ( 20 ) 頁： 31299 - 31304 2025年8月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

BaGe<inf>2</inf>O<inf>5</inf> III-type SrSi<inf>2</inf>O<inf>5</inf>:Eu<sup>2+</sup> in which the Sr<sup>2+</sup> site is 12-coordinated, the highest coordination number among strontium silicates, has been successfully synthesized under high pressure and temperature, 16 GPa and 900 °C for 60 min using an almost glassy starting sample. It is found that the glassy state of the starting sample is much more useful to form SrSi<inf>2</inf>O<inf>5</inf>:Eu<sup>2+</sup> under high temperature and pressure compared to conventional solid-state reaction using a crystalline multiphase starting sample. Photoluminescence and cathodoluminescence of the SrSi<inf>2</inf>O<inf>5</inf>:Eu<sup>2+</sup> major-phase sample have been investigated in the ambient temperature and pressure conditions. SrSi<inf>2</inf>O<inf>5</inf>:Eu<sup>2+</sup> exhibits an emission peak at 379 nm which is shorter than those of the reported Eu<sup>2+</sup>-activated strontium silicate phosphors such as Sr<inf>3</inf>SiO<inf>5</inf>:Eu<sup>2+</sup>, Sr<inf>2</inf>SiO<inf>4</inf>:Eu<sup>2+</sup>, and SrSiO<inf>3</inf>:Eu<sup>2+</sup>. This is attributable to the cuboctahedral coordination of SrO<inf>12</inf>, i.e., EuO<inf>12</inf> in the BaGe<inf>2</inf>O<inf>5</inf> III-type SrSi<inf>2</inf>O<inf>5</inf>:Eu<sup>2+</sup>, which is more isotropic due to the higher coordination number of the Eu<sup>2+</sup>-site than those of other phosphors and results in reducing the crystal field splitting of the 5d level of Eu<sup>2+</sup>.

DOI： 10.1016/j.ceramint.2025.04.317

Phase Transition of MnN(2) Associated with N(2) Dimer Alignment under High Pressure and High Temperature. 査読有り

Asano S, Niwa K, Yokoi T, Sasaki T, Kawaguchi-Imada S, Matsunaga K, Hasegawa M

Inorganic chemistry 64 巻 ( 22 ) 頁： 10700 - 10705 2025年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Manganese pernitride (MnN<inf>2</inf>) was synthesized at a pressure of approximately 60 GPa and a temperature of approximately 2000 K for the first time. A phase transition between rhombohedral and triclinic symmetry associated with the alignment of the N<inf>2</inf> dimer was also clearly observed at high temperatures under high pressure or along the decompression process at room temperature. The present experimental results with DFT calculations offer new insights and diversity into the crystal chemistry of the transition metal pernitrides concerning temperature and pressure.

DOI： 10.1021/acs.inorgchem.5c01118

High-pressure synthesis of PbN2, the missing group 14 AN2-type compound 査読有り国際共著国際誌 Open Access

Niwa K., Ogasawara H., Sasaki T., Nomura S., Azuma G., Pitié S., Frapper G., Hasegawa M.

Journal of Materials Chemistry A 13 巻 ( 26 ) 頁： 20588 - 20596 2025年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Chemistry A

The direct reaction of Pb with molecular nitrogen was investigated using a laser-heated diamond anvil cell combined with high-pressure in situ synchrotron X-ray powder diffraction measurements and Raman spectroscopy. From the results of the experiments and DFT calculations, it was revealed that a novel PbN<inf>2</inf> was successfully synthesized above 50 GPa, and it was observed to crystallize in a tetragonal system (indexation in the CuAl<inf>2</inf>-type structure, I4/mcm), comprising PbN<inf>8</inf> units connected via N-N dimers. Room-temperature compression and decompression experiments revealed that PbN<inf>2</inf> retained its structural integrity up to a pressure of approximately 90 GPa, while it decomposed into lead and nitrogen at around 15 GPa. The experimental evidence indicates that the encapsulated nitrogen dumbbells act as anionic units, (N<inf>2</inf>)<sup>2−</sup> interaction with the lead lattice. The newly synthesized PbN<inf>2</inf> exhibits a distinct crystal structure in comparison to the pyrite form of the other group-14 pernitrides (SiN<inf>2</inf>, GeN<inf>2</inf>, and SnN<inf>2</inf>) that have been previously reported. This finding provides novel insights into the high-pressure crystal chemistry of nitrogen-based compounds.

DOI： 10.1039/d5ta01488c

新規な14族元素窒素化合物の超高圧高温合成と結晶化学招待有り査読有り

丹羽健, 小笠原宏和, 山西正悟, 佐々木拓也, 長谷川正

日本結晶学会誌 66 巻 ( 4 ) 頁： 230 - 234 2024年12月

High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P4 国際誌 Open Access

Chang C.C., Sasaki T., Muto S., Gaida N.A., Niwa K., Hasegawa M.

Journal of Solid State Chemistry 340 巻頁： 125021 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Solid State Chemistry

Pseudo-ternary CrP<inf>4</inf>-type (V,Cr,Mo)P<inf>4</inf> 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)P<inf>4</inf> contains almost equimolar amounts of transition metals. The lattice parameters and unit cell volume of (V,Cr,Mo)P<inf>4</inf> 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)P<inf>4</inf>. While from the high-pressure (P < 10 GPa) in-situ synchrotron XRD measurements, it was found that (V,Cr,Mo)P<inf>4</inf> 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)P<inf>4</inf> and (V,Cr,Mo)P<inf>4</inf>, respectively. MoP<inf>6</inf> octahedral is highly distorted in comparison with VP<inf>4</inf> and CrP<inf>4</inf>, thus the incorporation of MoP<inf>4</inf> greatly yields incompressible behaviors of CrP<inf>4</inf>-type phosphides with respect to temperature and pressure.

DOI： 10.1016/j.jssc.2024.125021

Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe3 phase. 査読有り国際共著国際誌 Open Access

Journal of applied crystallography 57 巻 ( Pt 3 ) 頁： 755 - 769 2024年6月

High-Pressure Synthesis and Characterization of Novel Inorganic Compounds Open Access

Sasaki T.

Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu 34 巻 ( 2 ) 頁： 96 - 102 2024年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu

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 and low-temperature thermal expansion behavior of homogeneous phosphorus-rich pseudo-binary compound (V0.5Cr0.5)P4 査読有り国際誌

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

Ceramics International 49 巻 ( 24 ) 頁： 40990 - 40994 2023年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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. 国際共著国際誌 Open Access

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

Inorganic chemistry 62 巻 ( 49 ) 頁： 20271 - 20278 2023年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Synthesis of garnet-type Mn4+-activated Y3(Al,Ga)5O12 and (Y,Gd)3Al5O12 phosphors with controlled emission by cation substitution 査読有り国際誌

Sasaki, T; Asaka, R; Niwa, K; Gaida, NA; Hasegawa, M

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 131 巻 ( 10 ) 頁： 696 - 700 2023年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Ga- and Gd-substituted garnet-type Y3Al5O12:Mn4+ phosphors, Y3(Al11xGax)5O12:Mn4+ and (Y11yGdy)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(Al11xGax)5O12 and 380 % substituted (Y11yGdy)3Al5O12 (y ¯ 30.8) 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 査読有り国際誌

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

Progress in Solid State Chemistry 72 巻頁： 100426/1 - 100426/5 2023年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 査読有り国際誌

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

Materials Letters 347 巻 ( 15 ) 頁： 134601/1 - 134601/3 2023年9月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

新規遷移金属多窒化物の超高圧高温合成と圧縮および熱膨張特性招待有り査読有り

長谷川正, 浅野秀斗, 張仲景, 佐々木拓也, 丹羽健

熱測定 50 巻 ( 1 ) 頁： 13 - 19 2023年1月

High-pressure synthesis and crystal structures of molybdenum nitride Mo3N5 with anisotropic compressibility by a nitrogen dimer 査読有り国際誌

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

DALTON TRANSACTIONS 52 巻 ( 2 ) 頁： 469 - 475 2023年1月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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

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

Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu 33 巻 ( 1 ) 頁： 26 - 33 2023年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu

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

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

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

Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu 33 巻 ( 4 ) 頁： 254 - 260 2023年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Review of High Pressure Science and Technology Koatsuryoku no Kagaku to Gijutsu

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

超高圧力下での新物質・新結晶の溶液結晶成長査読有り

長谷川正, 佐々木拓也, Nico A. GAIDA, 丹羽健

日本結晶成長学会誌 49 巻 ( 2 ) 頁： n/a 2022年7月

High-pressure polycrystalline thin-film synthesis and semiconducting property of platinum pernitride 国際誌 Open Access

Niwa, K; Iizuka, T; Kurosawa, M; Nakamura, Y; Valencia, HO; Kishida, H; Nakatsuka, O; Sasaki, T; Gaida, NA; Hasegawa, M

AIP ADVANCES 12 巻 ( 5 ) 頁： 055318 - 055318 2022年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Aip Advances

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

　前のページ - 次のページ　

1
2
3