Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improvement of reversible H storage capacity by fine tuning of the
  composition in the pseudo-binary systems A2-xLaxNi7 (A = Gd, Sm, Y, Mg)   A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely
studied as active materials for negative electrode in Ni-MH batteries. By
playing on the substitution rate of both A and B elements, it is possible to
prepare various compositions. This strategy will help to improve the
properties, for example get a higher reversible hydrogen capacity and a
well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare
earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can
contain various late transition metals (Mn to Ni). To understand the effects of
composition on the physicochemical properties of La2Ni7-based compound, various
pseudo-binary systems have been investigated: Gd2 xLaxNi7 (x = 0, 0.6, 1, 1.5),
Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1,
1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their
crystallographic properties, X-ray diffraction analysis was performed followed
by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen
sorption were investigated at room temperature. Quaternary compounds present
drastically improved sorption properties in the frame of practical energy
storage applications with reversible capacity equivalent to 400 mAh/g for the
compound La1.1Sm0.5Mg0.4Ni7.

17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio