Neutron and X-ray diffraction profile analyses and structure of LaNi5, LaNi5−xAlx and LaNi5−xMnx intermetallics and their hydrides (deuterides)

Percheron-Guégan, A.; Lartigue, C.; Achard, Jocelyn; Germi, P.; Tasset, F.

doi:10.1016/0022-5088(80)90063-6

Cited by 243 publications

(84 citation statements)

References 9 publications

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“…The tetrahedral D2 positions are situated in the z ¼ 0:5 plane. As neutron diffraction studies by several researchers have shown, 11,12) the D1 positions start to be occupied first in the initial process of hydrogenation with giving the first plateau. Subsequently the tetrahedral D2 positions start to be occupied on the further hydrogenation giving the second plateau.…”

Section: Resultsmentioning

confidence: 96%

Hydrogenation and Dehydrogenation Properties of RHNi5 (RH = Heavy Rare Earth) Binary Intermetallic Compounds

et al. 2004

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We systematically investigated the hydrogenation and dehydrogenation properties for heavy rare earth-based binary R H Ni 5 (R H = Gd, Tb and Dy) intermetallic compounds and evaluated the correlations between crystallographic and thermodynamic properties. XRD analysis shows that all R H Ni 5 compounds crystallize in the hexagonal CaCu 5 -type crystal structure. In analogy to the light rare earth-based R L Ni 5 (R L = La, Pr, Nd and Sm) compounds both lattice constants of R H Ni 5 compounds decrease with increasing the atomic number of R H element due to the lanthanide contraction. On the pressure-composition (P-C) isotherms, GdNi 5 -H 2 system shows two well-separated pressure plateaux qualitatively similar to R L Ni 5 -H 2 systems. Looking over from Gd to Dy in the R H Ni 5 compounds, we find three specific dehydrogenation properties on the P-C isotherms: 1. The first plateau pressure (p P1 ) increases in this order (at around H/R H Ni 5 = 2.5) due to less stability of hydrogen in the unit cell by the lanthanide contraction. Linear correlations are also observed between log p P1 and the unit cell volume (V) which fall onto the same lines extrapolated from those observed in case of the R L Ni 5 compounds. 2. The second plateau (P2) tends to disappear because the P-C isotherm goes beyond the critical point of the phase transition. 3. Fairly flat first plateau separates into two parts in which a new plateau (PN) appears at low hydrogen content (H/R H Ni 5 2) with hysteretic phase transition. So long as the first plateau of dehydrogenation is concerned, from LaNi 5 to DyNi 5 we can predict the first plateau pressure from the unit cell volume of compounds and temperature.

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Section: Resultsmentioning

confidence: 96%

Hydrogenation and Dehydrogenation Properties of RHNi5 (RH = Heavy Rare Earth) Binary Intermetallic Compounds

et al. 2004

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“…Based on neutron diffraction analysis, several researchers [12][13][14] have proposed that on initial hydrogen absorption 75% of deuterium atoms occupy the D1 positions while 25% occupy the D2 positions. Assuming that the composition of the phase is RNi 5 H 4 , the D1 and D2 positions have three and one hydrogen atoms in the unit cell, respectively.…”

Section: Resultsmentioning

confidence: 99%

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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“…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. Therefore, the hydrogenation and dehydrogenation processes depend on the content of aluminum in the LaNi 5−x Al x -H 2 system.…”

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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Neutron and X-ray diffraction profile analyses and structure of LaNi5, LaNi5−xAlx and LaNi5−xMnx intermetallics and their hydrides (deuterides)

Cited by 243 publications

References 9 publications

Hydrogenation and Dehydrogenation Properties of R<SUB>H</SUB>Ni<SUB>5</SUB> (R<SUB>H</SUB> = Heavy Rare Earth) Binary Intermetallic Compounds

Hydrogenation and Dehydrogenation Properties of R<SUB>H</SUB>Ni<SUB>5</SUB> (R<SUB>H</SUB> = Heavy Rare Earth) Binary Intermetallic Compounds

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

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