Japan Metals and Chemicals Co.

Yamagata-shi, Japan

Japan Metals and Chemicals Co.

Yamagata-shi, Japan
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Iwase K.,Ibaraki University | Mori K.,Kyoto University | Terashita N.,Japan Metals and Chemicals Co. | Tashiro S.,Ibaraki University | Suzuki T.,Ibaraki University
Inorganic Chemistry | Year: 2017

The crystal structure of Pr3MgNi14D18 was determined by neutron diffraction. The determined structure of Pr3MgNi14D18 consisted of 89.0% Gd2Co7-type structure and 11.0% PuNi3-type structure. The lattice parameters of a and c of Gd2Co7-type structure were refined at 0.52903(7) nm and 3.90179(1) nm. The deuterium atoms were distributed among nine deuterium sites in both the CaCu5-type and MgZn2-type cells. The D2 occupancy in the Pr2Ni4 octahedral sites of the CaCu5-type cell was the largest (0.75) when compared with the other deuterium sites (<0.49). The deuterium content of the CaCu5-type cell showed 0.75 D/M, but the D/M value of the MgZn2-type cell was 1.53. The volume expansions during deuteration of the CaCu5-type and MgZn2-type cells were nearly equal. The cyclic hydrogenation property of Pr3MgNi14 is comparable to that of LaNi5. It is inferred that the similar expansion behavior of the CaCu5-type and MgZn2-type cells during deuteration is the origin of this cyclic stability. © 2017 American Chemical Society.


Park I.,University of Tokyo | Terashita N.,Japan Metals and Chemicals Co. | Abe E.,University of Tokyo
Journal of Alloys and Compounds | Year: 2013

Using transmission electron microscopy (TEM), we systematically investigate hydrogenation-induced microstructural changes of pseudo-binary (Pr xMg1-x)Ni2 Laves compounds varying x from 0.3 to 1.0, which lead to the averaged constituent atomic-size ratio RA/RB ranging 1.34-1.47 of the supposed AB2 compound. It is empirically known for the AB2 Laves compounds that hydrogen-induced-amorphization (HIA) takes place when the RA/R B exceeds 1.37. We find that, based on careful analyses of electron diffraction patterns and TEM images, the hydrogenation-processed microstructures of the (PrxMg1-x)Ni2 compounds exceeding the critical ratio are not pure amorphous but composed of Ni nano-crystals embedded in an amorphous matrix of hydride PrH2. This provides a direct evidence of hydrogenation-induced micro-phase separation (HIMPS), and accordingly it is suggested that HIA believed so far should be attributed to HIMPS phenomenon. © 2013 Elsevier B.V. All rights reserved.


Sakaki K.,Japan National Institute of Advanced Industrial Science and Technology | Terashita N.,Japan Metals and Chemicals Co. | Tsunokake S.,Japan Metals and Chemicals Co. | Nakamura Y.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

The effect of the rare earth elements and alloy composition on the hydrogenation properties and crystal structures of hydrides in Mg 2-xRE xNi 4 (RE = La, Pr, Nd, Sm, and Gd; x = 0.6 and 1.0) was investigated. All Mg 2-xRE xNi 4 alloys had a C15b Laves phase before hydrogenation. Mg 1.4RE 0.6Ni 4 (RE = Pr, Sm, and Gd) alloys were hydrogenated through one plateau to form Mg 1.4RE 0.6Ni 4H ∼3.6 while maintaining the C15b structure. Mg 1.0RE 1.0Ni 4 (RE = La, Pr, and Nd) alloys were hydrogenated to ∼1.0 H/M proceeding through two plateaus, and Mg 1.0RE 1.0Ni 4 (RE = Sm and Gd) alloys were hydrogenated to 0.6-0.7 H/M through one plateau. Mg 1.0RE 1.0Ni 4 alloys initially transformed into Mg 1.0RE 1.0Ni 4H ∼4 with an orthorhombic structure. In addition it was experimentally confirmed that Mg 1.0RE 1.0Ni 4H ∼4 with La, Pr, and Nd transformed into Mg 1.0RE 1.0Ni 4H ∼6 with a C15b structure, while no formation of Mg 1.0RE 1.0Ni 4H ∼6 (RE = Sm and Gd) was observed at 40 MPa at 250 K. Theoretical calculations suggest that Mg 1.0RE 1.0Ni 4H ∼4 with Sm and Gd also transform to Mg 1.0RE 1.0Ni 4H ∼6 at higher pressures than those used in our experiments (264 MPa for Mg 1.0Sm 1.0Ni 4 and 8.5 GPa for Mg 1.0Gd 1.0Ni 4 at 253 K). It was found that the hydrogenation properties and crystal structure of the hydrides in Mg 2-xRE xNi 4 are dependent on the alloy composition, i.e., the ratio of Mg to RE in the alloy phase, but independent of the choice of rare earth element. © 2012 American Chemical Society.


Iwase K.,Ibaraki University | Terashita N.,Japan Metals and Chemicals Co. | Mori K.,Kyoto University | Tsunokake S.,Japan Metals and Chemicals Co. | Ishigaki T.,Ibaraki University
International Journal of Hydrogen Energy | Year: 2012

We investigated the crystal structure and cyclic hydrogen absorption-desorption properties of Pr 2MgNi 9. The structural model is based on the PuNi 3-type structure; the Mg atom is assumed to substitute for the Pr site in an MgZn 2-type cell. The refined lattice parameters were determined from X-ray diffraction. A wide plateau region was observed in the P-C (pressure composition) isotherm at 298 K. The maximum hydrogen capacity reached 1.12 H/M (1.62 mass%) under a hydrogen pressure of 2.0 MPa. After 1000 hydrogen absorption-desorption cycles, the hydrogen capacity was superior to that of LaNi 5 (82%). Anisotropic lattice strain occurred in the hydriding process. The anisotropic peak-broadening vector was determined to be <001>. The calculated anisotropic lattice strains of the initial cycle and after 1000 cycles were far smaller than those of LaNi 5. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Sakaki K.,Japan National Institute of Advanced Industrial Science and Technology | Terashita N.,Japan Metals and Chemicals Co. | Tsunokake S.,Japan Metals and Chemicals Co. | Nakamura Y.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

The phase transformations of Mg 1.4Pr 0.6Ni 4 and Mg 1.0Pr 1.0Ni 4 during hydrogenation and dehydrogenation were investigated using in situ X-ray diffraction (XRD). Both alloys showed the cubic MgCu 4Sn type structure with space group F4̄3m before hydrogenation. The hydride β-Mg 1.4Pr 0.6Ni 4H ∼3.6 had the same crystal structure as the starting alloy, and its lattice was expanded by 4.3% by hydrogenation. Mg 1.0Pr 1.0Ni 4 was initially transformed to an orthorhombic β-Mg 1.0Pr 1.0Ni 4H ∼4 with space group Pmn2 1. By further hydrogenation, the orthorhombic hydride changed to β-Mg 1.0Pr 1.0Ni 4H ∼6 with a cubic structure with space group F4̄3m. The lattice constant of β-Mg 1.0Pr 1.0Ni 4H ∼6 was 7.6% larger than that of the starting alloy. Through dehydrogenation, all hydride phases returned to the alloy phase without any amorphization or disproportionation. © 2011 American Chemical Society.


Sakaki K.,Japan National Institute of Advanced Industrial Science and Technology | Terashita N.,Japan Metals and Chemicals Co. | Kim H.,Japan National Institute of Advanced Industrial Science and Technology | Proffen T.,Los Alamos National Laboratory | And 5 more authors.
Inorganic Chemistry | Year: 2013

We studied crystal structure and local structure of Mg2-xPr xNi4 (x = 0.6 and 1.0) and their deuterides using in situ neutron total scattering and first-principles calculations. The total scattering data were analyzed using Rietveld refinement and pair distribution function analysis (PDF). The crystal structure of Mg2-xPrxNi 4 before deuterium absorption was C15b in space group F4̄3m. No difference between the crystal and local (PDF) structures was observed. The crystal structure of Mg1.0Pr1.0Ni4D ∼4 was found to be orthorhombic in space group Pmn21, with three deuterium occupation sites: PrNi3 and two types of bipyramidal Pr2MgNi2 that have a plane of symmetry composed of MgNi2. There is no significant difference between the crystal structure and the local structure of Mg1.0Pr 1.0Ni4D∼4. On the other hand, the average crystal structure of the Mg-rich Mg1.4Pr0.6Ni 4D∼3.6 was C15b with two deuterium occupation sites: PrNi3 and MgPrNi2 suggesting that the deuterium occupation shifts away from the Pr2MgNi2 bipyramid. First-principles relaxed structures also showed the shift of the hydrogen occupation site toward the Pr atom of the bipyramid, when induced by Mg substitution for the opposing Pr, resulting in hydrogen occupation in the MgPrNi2 tetrahedral site. The PDF pattern of Mg1.4Pr0.6Ni4D ∼3.6 cannot be refined below 7.2 Å in atomic distances using the C15b structure which was obtained from Rietveld refinement but can be done using an orthorhombic structure. It suggests that Mg1.4Pr 0.6Ni4D∼3.6 was locally distorted to the orthorhombic. © 2013 American Chemical Society.


Iwase K.,Ibaraki University | Terashita N.,Japan Metals and Chemicals Co. | Mori K.,Kyoto University | Yokota H.,Ibaraki University | Suzuki T.,Ibaraki University
Inorganic Chemistry | Year: 2013

The hydrogen absorption-desorption property and the crystal structure of Pr4MgNi19 was investigated by pressure-composition isotherm measurement and X-ray diffraction (XRD). Pr4MgNi 19 consisted of two phases: 52.9% Ce5Co19-type structure (3R) and 47.0% Gd2Co7-type structure (3R). Sm5Co19-type structure (2H) and Ce2Ni 7-type structure (2H) were not observed in the XRD profile. The Mg atoms substituted at the Pr sites in a MgZn2-type cell. The maximum hydrogen capacity reached 1.14 H/M (1.6 mass%) at 2 MPa. The hysteresis factor, Hf = ln(Pabs/Pdes), was 1.50. The cyclic hydrogenation property of Pr4MgNi19 was investigated up to 1000 absorption-desorption cycles. After 250, 500, 750, and 1000 cycles, the retention rates of hydrogen were reduced to 94%, 92%, 91%, and 90%, respectively. These properties were superior to those of Pr2MgNi 9 and Pr3MgNi14. © 2013 American Chemical Society.


Kim H.,Japan National Institute of Advanced Industrial Science and Technology | Sakaki K.,Japan National Institute of Advanced Industrial Science and Technology | Ogawa H.,Japan National Institute of Advanced Industrial Science and Technology | Nakamura Y.,Japan National Institute of Advanced Industrial Science and Technology | And 5 more authors.
Journal of Physical Chemistry C | Year: 2013

Reduction in reversible hydrogen storage capacity with increasing hydrogenation and dehydrogenation cycle number is observed in numerous hydrogen storage materials, but the mechanism behind this unfavorable change has not been elucidated yet. In this study, we have investigated the development of structural defects or disorders in V1-xTixH2, x = 0, 0.2, and 0.5, during the first 15 hydrogen absorption and desorption cycles using the atomic pair distribution function (PDF) analysis of synchrotron X-ray total scattering data to find out the possible structural origin of the poor cyclic stability of V1-xTix alloys. While pure vanadium shows no significant change in the PDF, alloy samples subject to several hydrogenation and dehydrogenation cycles display fast decaying of the PDF profile due to a progressive increase in the PDF peak width with increasing r. This r-dependent PDF peak broadening effect becomes stronger with cycle number. Molecular dynamics (MD) simulations demonstrated that dislocation defects explain characteristic features in our experimental PDFs very well and suggested that a large number of dislocations are formed during hydrogen cycling. We found there is a close relation between the reduced amount of the reversible hydrogen content of V0.8Ti0.2 and the amount of generated dislocations. On the basis of the PDF analysis results, a possible mechanism behind degradation in the reversible hydrogen storage capacity of V1-xTix is discussed. © 2013 American Chemical Society.


Terashita N.,Japan Metals and Chemicals Co. | Sakaki K.,Japan National Institute of Advanced Industrial Science and Technology | Tsunokake S.,Japan Metals and Chemicals Co. | Nakamura Y.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Materials Transactions | Year: 2012

Ternary intermetallic compounds, Mg 2-xPr xNi 4 (0.6 ≤ x ≤ 1.4) were synthesized by induction melting and investigated with respect to hydrogenation properties and structural changes. These compounds have a cubic C15 b-type Laves structure (space group F-43m), where Mg and Pr have an ordered arrangement. The lattice parameters increased from a = 0.70101(3)nm to a = 0.71726(8)nm with increase of the Pr content. Mg 1.4Pr 0.6Ni 4 and Mg 1.2Pr 0.8Ni 4 absorbed and desorbed hydrogen up to ∼0.7 H/M reversibly through one plateau in the p-c isotherms. The stoichiometric MgPrNi 4 showed two plateaus and its maximum hydrogen content reached to ∼1.0 H/M at 35MPa. The enthalpy changes of hydrides formation of Mg 1.4Pr 0.6Ni 4 and Mg 1.2Pr 0.8Ni 4 were estimated to be -39.2 and -40.3 kJ/mol H 2 respectively. The enthalpy changes of hydrides formation of MgPrNi 4 at the lower and higher plateaus were estimated to be -42.4 and -19.6 kJ/mol H 2 respectively. The metal sublattice of hydrides Mg 1.4Pr 0.6Ni 4H ∼4 and Mg 1.2Pr 0.8Ni 4H ∼4 had cubic ordered C15 b-type Laves structure same as the crystal structure before hydrogenation while hydride at the lower plateau of the stoichiometric MgPrNi 4 had an orthorhombic structure. The hydrogenation of Mg 0.8Pr 1.2Ni 4 and Mg 0.6Pr 1.4Ni 4 led to amorphization. © 2012 The Japan Institute of Metals.


Iwase K.,Ibaraki University | Terashita N.,Japan Metals and Chemicals Co. | Mori K.,Kyoto University | Ishigaki T.,Ibaraki University
Inorganic Chemistry | Year: 2012

Structural parameters of Pr 3MgNi 14 after a cyclic hydrogen absorption-desorption process were investigated by X-ray diffraction. Pr 3MgNi 14 consisted of two phases: 80% Gd 2Co 7-type structure and 20% PuNi 3-type structure. The pressure-composition (P-C) isotherm of Pr 3MgNi 14 indicates a maximum hydrogen capacity of 1.12 H/M (1.61 mass%) at 298 K. The cyclic property of Pr 3MgNi 14 up to 1000 cycles was measured at 313 K. The retention rate of the sample was 87.5% at 1000 cycles, which compares favorably with that of LaNi 5. After 1000 cycles, the expansions of lattice parameters a and c and the lengths along the c-axes of the PrNi 5 and PrMgNi 4 cells of the Gd 2Co 7-type structures were 0.20%, 1.26%, 0.47%, and 3.68%, respectively. The metal sublattice expanded anisotropically after the cyclic test. The isotropic and anisotropic lattice strains can be refined by Rietveld analysis. The anisotropic and isotropic lattice strains were almost saturated at the first activation process and reached values of 0.2% and 0.1%, respectively, after 1000 cycles. These values are smaller by 1 order of magnitude than those of LaNi 5. © 2012 American Chemical Society.

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