| 1. |
- Denys, R. V., et al.
(författare)
-
Crystal chemistry and thermodynamic properties of anisotropic Ce2Ni7H4.7 hydride
- 2007
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 180:9, s. 2566-2576
-
Tidskriftsartikel (refereegranskat)abstract
- A new intermetallic deuteride Ce2Ni7D4.7 with an anomalous volume expansion has been studied. Its structure was solved on the basis of in situ neutron diffraction data. Expansion proceeds along the c-axis and within the CeNi2 slabs only. All D atoms are located inside these slabs and on the border between CeNi2 and CeNi5. Ordering of D atoms in the bulk of CeNi2 is accompanied by substantial deformation of these slabs thus lowering the hexagonal symmetry to orthorhombic [space group Pmcn (No. 62); a = 4.9251(3) angstrom b = 8.4933(4) angstrom, c = 29.773(1) angstrom]. Inside the CeNi2 layer the hydrogen sublattice is completely ordered; all D-D distances exceed 2.0 angstrom Local coordination of Ni by D inside the CeNi, blocks is of "open", saddle-like type. Hydrogen ordering is mainly determined by Ce-H and H-H interactions. The press ure-composition-temperature measurements yielded the following thermodynamic parameters of the formation of the hydride: Delta H = -22.4 kJ/MOl(H), Delta S = -59.9 J/(K mol(H)).
|
|
| 2. |
- Denys, R. V., et al.
(författare)
-
Mg substitution effect on the hydrogenation behaviour, thermodynamic and structural properties of the La2Ni7-H(D)(2) system
- 2008
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 181:4, s. 812-821
-
Tidskriftsartikel (refereegranskat)abstract
- The present work is focused on studies of the influence of magnesium on the hydrogenation behaviour of the (La,Mg)(2)Ni-7 alloys. Substitution of La in La2Ni7 by Mg to form La1.5Mg0.5Ni7 preserves the initial Ce2Ni7 type of the hexagonal P6(3)/mmc structure and leads to contraction of the unit cell. The system La1.5Mg0.5Ni7-H2 (D-2) was studied using in situ synchrotron X-ray and neutron powder diffraction in H-2/D-2 gas and pressure-composition-temperature measurements. La replacement by Mg was found to proceed in an ordered way, only within the Laves-type parts of the hybrid crystal structure, yielding formation of LaMgNi4 slabs with statistic and equal occupation of one site by La and Mg atoms. Mg alters structural features of the hydrogenation process. Instead of a strong unilateral anisotropic expansion which takes place on hydrogenation of La2Ni7, the unit cell of La1.5Mg0.5Ni7D9.1 is formed by nearly equal hydrogen-induced expansions proceeding in the basal plane (Delta a/a = 7.37%) and along [001] (Delta c/c = 9.67%). In contrast with La2Ni7D6.5 where only LaNi2 layers absorb hydrogen atoms, in La1.5Mg0.5Ni7D9.1 both LaNi5 and LaMgNi4 layers become occupied. Nine types of sites were found to be filled by D in total, including tetrahedral (La,Mg)(2)Ni-2, (La,Mg)Ni-3, Ni-4, tetragonal pyramidal La2Ni3 and trigonal bipyramidal (La,Mg)(3)Ni-2 interstices. The hydrogen sublattice around the La/Mg site shows formation of two co-ordination spheres of D atoms: an octahedron MgD6 and a 16-vertex polyhedron LaD16 around La. The interatomic distances are in the following ranges: La-D (2.28-2.71), Mg-D (2.02-2.08), Ni-D (1.48-1.86 angstrom). All D-D distances exceed 1.9 angstrom. Thermodynamic PCT studies yielded the following values for the Delta H and Delta S of hydrogenation/decomposition; Delta H-H = -15.7 +/- 0.9 kJ (mol(H))(-1) and Delta S-H = -46.0 +/- 3.7 J (K mol(H))(-1) for H-2 absorption, and Delta H-H = 16.8 +/- 0.4 kJ (mol(H))(-1) and Delta S-H = 48.1 +/- 1.5 J (K mol(H))(-1) for H-2 desorption.
|
|
| 3. |
- Denys, R. V., et al.
(författare)
-
Hydrogen storage properties and structure of La1-xMgx(Ni1-yMny)(3) intermetallics and their hydrides
- 2007
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 446, s. 166-172
-
Tidskriftsartikel (refereegranskat)abstract
- 'Hybrid' RNi3 (R =rare earth metal) crystal structures are built of the slabs of simpler types, CaCu5 and MgZn2. Different affinities of these slabs to hydrogen result in unusual "anisotropic" expansion of the RNi3 and R2Ni7 (R = La, Cc) structures upon hydrogenation. This work focuses on studies of the hydrogenation behaviour of LaNi3 and on the properties of the hydrides of the modified by Mg and Mn La-Ni alloys. The crystal structure of LaNi3D2.8 and the crystal structure and hydrogen storage behaviours of the La1.5Mg0.5Ni7 and La(Ni-1-,Mn,)3 (x=0; 0.067-, 0.133; 0.2: 0.267; 0.3; 0.333; 0.4) alloys were in focus. The deuteration of LaNi3 with PuNi3 type of structure leads to the formation of LaNi3D2.8 and is accompanied by a deformation of the metal matrix causing a change of the initial rhombohedral symmetry (space group R3m) to a nionoclinic one (space group C2/m; a = 8.6408(7) angstrom, b=4.928](4) angstrom, c= 32.774(3) A; = 90.850(8)degrees; V= 1395.5(2) angstrom(3)). Similar to the earlier studied CeNi3D2.8, preferential occupation by deuterium atoms of the AB, layers takes place, leading to the "anisotropic" expansion of the unit cell along [0 0 1] (Delta c/c = 30.6%). 14 occupied D crystallographic sites have 4 chemically different types of metal-atom surroundings, including Ni-4 (2), La2Ni2 (2), La3Ni (6), and La3Ni3 (4). Modification of the La-Ni alloys by magnesium and manganese leads to the formation of intermetallic compounds crystallising with the PuNi3, CeNi3, and Ce2Ni7-type structures. An ordered substitution of La by Mg in the MgZn2-type slabs was observed, causing a complete alteration of the hydrogenation behaviour of the original LaNi3 alloy. La1.5Mg0.5Ni7D9 isotropically expands upon its formation and leads to a substantial increase of the stability against hydrogenation-induced aniorphisation. On the other hand, replacement of Ni by Mn leads to the change in crystal-structure type from PuNi3 to CeNi3 in the LaNi3-xMn. alloys (x>0.1). An ordered substitution of Ni by Mn proceeds inside the RNi5 slabs only. This decreases the stability of the initial alloy against amorphisation on hydrogenation.
|
|
| 4. |
- Nazer, N. S., et al.
(författare)
-
In operando neutron diffraction study of LaNdMgNi9H13 as a metal hydride battery anode
- 2017
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 343, s. 502-512
-
Tidskriftsartikel (refereegranskat)abstract
- La2MgNi9-related alloys are superior metal hydride battery anodes as compared to the commercial AB5 alloys. Nd-substituted La2-yNdyMgNi9 intermetallics are of particular interest because of increased diffusion rate of hydrogen and thus improved performance at high discharge currents. The present work presents in operando characterization of the LaNdMgNi9 intermetallic as anode for the nickel metal hydride (Ni-MH) battery. We have studied the structural evolution of LaNdMgNi9 during its charge and discharge using in situ neutron powder diffraction. The work included experiments using deuterium gas and electrochemical charge-discharge measurements. The alloy exhibited a high electrochemical discharge capacity (373 mAh/g) which is 20% higher than the AB5 type alloys. A saturated β-deuteride synthesized by solid-gas reaction at PD2 = 1.6 MPa contained 12.9 deuterium atoms per formula unit (D/f.u.) which resulted in a volume expansion of 26.1%. During the electrochemical charging, the volume expansion (23.4%) and D-contents were found to be slightly reduced. The reversible electrochemical cycling is performed through the formation of a two-phase mixture of the α-solid solution and β-hydride phases. Nd substitution contributes to the high-rate dischargeability, while maintaining a good cyclic stability. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the anode electrode on cycling. A mathematical model for the impedance response of a porous electrode was utilized. The EIS showed a decreased hydrogen transport rate during the long-term cycling, which indicated a corresponding slowing down of the electrochemical processes at the surface of the metal hydride anode.
|
|
| 5. |
- Pasquini, Luca, et al.
(författare)
-
Magnesium- and intermetallic alloys-based hydrides for energy storage : modelling, synthesis and properties
- 2022
-
Ingår i: Progress in Energy. - : Institute of Physics Publishing (IOPP). - 2516-1083. ; 4:3
-
Forskningsöversikt (refereegranskat)abstract
- Hydrides based on magnesium and intermetallic compounds provide a viable solution to the challenge of energy storage from renewable sources, thanks to their ability to absorb and desorb hydrogen in a reversible way with a proper tuning of pressure and temperature conditions. Therefore, they are expected to play an important role in the clean energy transition and in the deployment of hydrogen as an efficient energy vector. This review, by experts of Task 40 'Energy Storage and Conversion based on Hydrogen' of the Hydrogen Technology Collaboration Programme of the International Energy Agency, reports on the latest activities of the working group 'Magnesium- and Intermetallic alloys-based Hydrides for Energy Storage'. The following topics are covered by the review: multiscale modelling of hydrides and hydrogen sorption mechanisms; synthesis and processing techniques; catalysts for hydrogen sorption in Mg; Mg-based nanostructures and new compounds; hydrides based on intermetallic TiFe alloys, high entropy alloys, Laves phases, and Pd-containing alloys. Finally, an outlook is presented on current worldwide investments and future research directions for hydrogen-based energy storage.
|
|
| 6. |
- Yartys, V. A., et al.
(författare)
-
Crystal and magnetic structure of TbNiSnD studied by neutron powder diffraction
- 2007
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 311:2, s. 639-643
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structure of TbNiSnD has been studied by neutron powder diffraction. The deuteride crystallizes with the filled TiNiSi type structure (sp. gr. Pnma; a=7.0354(1); b=4.20662(9); c=8.1808(2) Å at 293 K; a=7.008(1); b=4.1954(6); c=8.153(1) Å at 2 K) and is canted ferromagnetic below 10 K. The deuterium atoms occupy the tetrahedral Tb3Ni sites. The Tb atoms carry a magnetic moment of 6.6(1) μB /Tb. They order antiferromagnetically along the a-axis and ferromagnetically along the c-axis. No significant magnetic moment on the Ni atoms has been observed by neutron diffraction. Insertion of deuterium in TbNiSn induces both a change of the magnetic structure and a reduction of the Tb magnitude of the magnetic moment.
|
|
