A new hydride phase of LaNi5H3

Akiba, Etsuo; Nomura, K.; Ono, Seigo

doi:10.1016/0022-5088(87)90043-9

Cited by 71 publications

(32 citation statements)

References 11 publications

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“…10) In the middle sets, there are some specific peaks, especially at lower angles such as 19. 4 , 19.7 , 34.1 , and 34.7 . All diffraction peaks of the phase are indexed according not to orthorhombic but to monoclinic structure (C2=m), which is the same as that of the phase in the PrNi 5 -H system.…”

Section: Resultsmentioning

confidence: 98%

“…The crystal structures of these phases are hexagonal, as shown by in-situ X-ray diffractometry (XRD), but with different lattice parameters. 3,4) In the PrNi 5 -H system 5) two well-separated pressure plateaux are present due to two different hydrides, with compositions of PrNi 5 H 4 ( phase) and PrNi 5 H 6 ( phase). Although the phase with hexagonal structure in the PrNi 5 -H system is similar to that in the LaNi 5 -H system, the structure of the phase in the PrNi 5 -H system is classified as C-centered monoclinic lattice.…”

Section: Introductionmentioning

confidence: 99%

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Structural Changes in RNi5-H (R = Pr, Nd, Sm and Gd) Systems with Two Hydrogen Pressure Plateaux

2004

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Pressure-composition (P-C) isotherms of RNi 5 -H (R = Pr, Nd, Sm and Gd) systems show two hydrogen pressure plateaux during hydrogen absorption and desorption. These correspond to the transitions among three phases: one hydrogen solid solution ( phase; RNi 5 H $0:5 ) and two hydrides ( phase; RNi 5 H 3$4 and phase; RNi 5 H 5$7 ). To explore the mechanism of the phase transitions, we investigated the structural changes in RNi 5 -H systems with ex-situ XRD. During hydrogen desorption, the ex-situ XRD profiles show that the crystal structures in RNi 5 -H systems change from hexagonal ( phase) through monoclinic ( phase) to hexagonal ( phase). The temporary decrease in structural symmetry may be due to hydrogen occupation except in the basal plane of the crystal structure. Lattice expansion between the and phases normalized in the monoclinic structure decreases slightly with the increasing atomic number of R in RNi 5 -H systems. Similarly to the correlation between the first plateau pressure and the unit cell volume of the phase, the second plateau pressure is logarithmically related to the unit cell volume of the phase. As far as the RNi 5 -H (R: from La to Gd except Ce) system is concerned, we can empirically predict the second plateau pressure as well as the first plateau pressure from the unit cell volume of the alloys.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Structural Changes in RNi5-H (R = Pr, Nd, Sm and Gd) Systems with Two Hydrogen Pressure Plateaux

2004

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“…1,2) Furthermore, it was reported that with the substitution of aluminum for nickel in LaNi 5 the lattice constant increases, 1) while the dislocation density 3) and the vacancy concentration 4) induced by hydrogenation decrease. In the LaNi 5 -H 2 system, the intermediate β phase (hydride LaNi 5 H 3 ) between the α phase (solid solution) and the γ phase (full hydride LaNi 5 H 6 ) forms in the desorption process above 343 K and in the absorption process above 367 K. [5][6][7] However, in the LaNi 5−x Al x -H 2 (x ≥ 0.1) system no intermediate hydride phase forms. 8) Furthermore, in-situ X-ray measurement 9) and neutron diffraction measurements [10][11][12][13][14] have shown that the space group of the solid solution and of the full hydride phase of LaNi 5−x Al x (x = 0.25, 0.5, 1.0) is P6/mmm, whereas the space group of the full hydride phase of LaNi 5 is P6 3 mc.…”

Section: Introductionmentioning

confidence: 99%

Hydrogenation and Dehydrogenation Behavior of LaNi5-xAlx (x=0-0.5) Alloys Studied by Pressure Differential Scanning Calorimetry

2002

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The hydrogenation and dehydrogenation behavior of LaNi 5−x Al x (x = 0-0.5) was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1 to 5 MPa in the temperature range from 323 to 573 K with the heating and cooling rates of 2 to 30 K min −1 . In the heating runs of the hydride with x ≤ 0.1 two endothermic peaks were observed. With the increase in the aluminum content, the first peak at lower temperature decreased, while the second peak at higher temperature increased. Furthermore, the difference in the temperatures of the peak top decreased with the increase in the aluminum content. In the heating runs of the hydride with x > 0.1 only one endothermic peak was observed. These endothermic peaks shifted to higher temperatures with the increase in the hydrogen pressure. Using Ozawa's method, the activation energies for dehydrogenation and hydrogenation processes were estimated. The activation energy for the dehydrogenation process of the hydrides increased with the increase in the hydrogen pressure and the aluminum content. However, the dependence of the activation energy on the aluminum concentration in the range of x ≥ 0.1 was different from that of x < 0.1. The activation energy for the hydrogenation process was estimated only in the range of x > 0.1 at the hydrogen pressure of 5 MPa. The value of activation energy for the hydrogenation was lower than that for the dehydrogenation.

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“…Consequently, the 6m site cannot be ruled out with its hole radius of about 0.551 Å [19]. It has been observed that the β -phase (hydride LaNi 5 H 3 ) is formed between the α -phase (solid solution) and the γ -phase (hydride LaNi 5 H 6 ) in the desorption process above 343 K and in the absorption process above 367 K [22,23].…”

Section: Application To Rni 5 -H 2 Systems and Discusionmentioning

confidence: 99%

Thermodynamical Modeling of P-C Isotherms for Metal Hydride Materials

Tserolas¹,

Katagiri²,

Onodera³

et al. 2010

Trans. Mat. Res. Soc. Japan

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It is generally accepted that under ordinary conditions adopted for the study of metal-hydrogen (M-H) compounds: a) hydrogen can be described reasonably well as an ideal gas, b) the distribution of hydrogen atoms over the different sites of the lattice can be expressed by the Fermi-Dirac statistics, c) the average hydrogen-hydrogen interaction energy which is a function of the number of H-atoms in the lattice includes all the contributions coming from the electrons and the lattice. By considering all the above approximations we have derived a relation between the pressure of gaseous hydrogen and the number of hydrogen atoms in the bulk. The PCIs were obtained by calculating the standard chemical potential for an ideal gas from statistical mechanics and optimizing the other free parameters from the experimental PCIs data at one temperature. We were able to closely predict the PCIs at other temperatures when they were compared with the experimentally obtained PCIs for various RNi 5 -type hydrogen storage materials.

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A new hydride phase of LaNi5H3

Cited by 71 publications

References 11 publications

Structural Changes in RNi<SUB>5</SUB>-H (R = Pr, Nd, Sm and Gd) Systems with Two Hydrogen Pressure Plateaux

Structural Changes in RNi<SUB>5</SUB>-H (R = Pr, Nd, Sm and Gd) Systems with Two Hydrogen Pressure Plateaux

Hydrogenation and Dehydrogenation Behavior of LaNi<SUB>5-x</SUB>Al<SUB>x</SUB> (x=0-0.5) Alloys Studied by Pressure Differential Scanning Calorimetry

Thermodynamical Modeling of P-C Isotherms for Metal Hydride Materials

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