Transmission electron microscopy study of order-disorder phenomena in non-stoichiometric LaNi5+x and LaNi6-xCux electrode materials

W.M.J.M. Coene, P.H.L. Notten, F. Hakkens, R.E.F. Einerhand, J.L.C. Daams

Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

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High-energy electron diffraction, X-ray powder diffraction and high-resolution electron microscopy have been used to investigate the crystallographic properties of non-stoichiometric LaNi5+x (0= =0.4) and LaNi6-xCux (0= =3.0) electrode materials, which are based on the CaCu5 structure type. Structural aspects with respect to Ni/Cu rich deviations from the exact AB5 stoichiometry are studied. X-ray powder diagrams show only the basic CaCu5 diffraction lines without any superstructure lines, and are therefore interpreted in terms of random substitutions of A atoms (La) by dumbbell pairs of B atoms (Ni/Cu) oriented along the c axis, thereby leading to a contraction and expansion of the lattice in the a and c direction, respectively. The observation of diffuse scattering in electron diffraction, which is located on a specific geometry in diffraction space, reveals that a large amount of the substitutions of A atoms by B2 dumbbells occur in a partially ordered manner. High-resolution electron microscopy shows that small Ni/Cu rich domains exist, in which the ordering is related to the stacking of A atoms and B2 dumbbells in the ordered rhombohedral and hexagonal A2B17 superstructures, and in the tetragonal AB12 superstructure.
Originele taal-2Engels
Pagina's (van-tot)1485-1502
TijdschriftPhilosophical Magazine A : physics of condensed matter, structure, defects and mechanical properties
Volume65
Nummer van het tijdschrift6
DOI's
StatusGepubliceerd - 1992

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