Electron Diffraction study of Layer Structures in La-Mg-Ni Hydrogen Absorption Alloys

Abstract

In order to improve the hydrogen absorption properties of the layer structure appearing at the nickel rich side of La-Mg-Ni alloy, appropriate amounts of Ni were replaced by some elemental atoms, Mn, Co and Al. The La 0:8 Mg 0:2 Ni 3:4Àx Co 0:3 (MnAl) x (0 < x < 0:4) alloy system was synthesized and crystal structures were investigated by electron microscopy. The atomic concentration ratio of (LaMg) to the other atoms was 3.7 in this system. The Pr 5 Co 19 -type structure (5:19H-structure) and the Ce 5 Co 19 -type structure (5:19R-structure) were found in this alloy system. Electron micrographs of these structures are presented in this paper. Structure analysis of the complex layer structure is demonstrated by careful observation of the electron diffraction pattern.

Stacking Faults and a Novel Structural Polytype in a Hydrogen-Storage (La<SUB>0.8</SUB>Mg<SUB>0.2</SUB>)Ni<SUB>3.5</SUB> Alloy with Block-Stacking Superstructures

“…In fact, an incommensurate structure due to the mixture of two block-types, n ¼ 5 and 6, appears in (La 0:8 Mg 0:2 )-(Ni 3:4Ài -Co 0:3 (AlMn) i ) (0 < i < 0:4) alloys with the off-stoichiometry compositions (m ¼ 3:7). 20) However, intra-block-layer faults are found to be quite rare for the present offstoichiometric (La 0:8 Mg 0:2 )Ni 3:5 alloy; instead, the interblock-layer type faults, which do not change the local composition, are frequently observed (Fig. 2(a)).…”

The Formation Mechanism and Electrochemical Cyclic Stability of the Single-Phase PrnMgNi5n-1(n= 2, 3, 4) Hydrogen Storage Alloy

“…7 illustrates the XRD patterns of the single-phase alloy powders before activation and after 50, 100 charge/discharge cycles. It can A2278 Journal of The Electrochemical Society, 163 (10) A2273-A2281 (2016) be seen the alloy powders still keep their original phase structures after cycling. While with the increasing of the cycle numbers, the intensity and width of the major diffraction peaks gradually become weaker and broader, respectively.…”

“…6,7 Depending on the stacking manner of [REMgNi 4 ] and [RENi 5 ] subunits, each of the alloy phase has an allotrope with either a hexagonal (2H) structure or a rhombohedral (3R) structure, such as CeNi 3 -(2H), PuNi 3 -(3R), Gd 2 Co 7 -(3R), Ce 2 Ni 7 -(2H), Pr 5 Co 19 -(2H), Ce 5 Co 19 -type (3R) superlattice structures. [8][9][10][11][12][13] In recent years, the ternary Pr-Mg-Ni-based alloys have been obtained by an annealing or a powder sintering method, and they possess good hydrogen storage capacity and show outstanding solid-gas cyclic stability comparing with the La-Mg-Ni-based alloys. Lemort et al 14 reported the hydrogenation features of the Pr 1.5 Mg 0.5 Ni 7 and Pr 3.75 Mg 1.…”

Cobalt-free Materials for Nickel-metal Hydride Battery: Self-discharge Suppression and Overdischarge-resistance Improvement

“…Patterns (a) and (b) were observed in different regions of an alloy#1 grain. Each of the patterns was indexed on the basis of the hexagonal 5:19H and rhombohedral 5:19R structures, 26 respectively. Alloy#1 contained multiple stacking-structured phases.…”