Transmission electron microscopy study of order-disorder phenomena in non-stoichiometric LaNi5+xand LaNi6-xCuxelectrode materials
- 1 June 1992
- journal article
- research article
- Published by Taylor & Francis in Philosophical Magazine A
- Vol. 65 (6) , 1485-1502
- https://doi.org/10.1080/01418619208205618
Abstract
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 AB 5 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 B 2 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 B 2 dumbbells in the ordered rhombohedral and hexagonal A 2B17 superstructures, and in the tetragonal AB 12 superstructure.Keywords
This publication has 17 references indexed in Scilit:
- Structure defects in rare-earth-iron carbides with the hexagonal Th2Ni17 structure type: A study by means of high resolution electron microscopyJournal of Solid State Chemistry, 1991
- Relationship between ThMn12 and Th2Ni17 structure types in the YFe11−xTix alloy seriesJournal of Applied Physics, 1990
- High energy electron diffraction and X-ray diffraction studies on magnetic materials of the type Y2Fe17Cx (0 ⩽ x ⩽ 1.6)Journal of the Less Common Metals, 1990
- High-resolution structure imaging of partially disordered atomic columns in binary alloy systemsPhilosophical Magazine Part B, 1987
- The real space method for dynamical electron diffraction calculations in high resolution electron microscopy: III. A computational algorithm for the electron propagation with its practical applicationsUltramicroscopy, 1984
- The cobalt-rich regions of the samarium-cobalt and gadolinium-cobalt phase diagramsJournal of the Less Common Metals, 1973
- X-ray and neutron determination of a so-called Th2Ni17-type structure in the lutetium-iron systemJournal of the Less Common Metals, 1972
- Phase relations and hydrogen absorption in the lanthanum-nickel systemJournal of the Less Common Metals, 1972
- Composition and crystal structure of hexagonal Cu-rich rare earth–copper compoundsActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 1971
- Intermetallic compounds in the system samarium-cobaltJournal of the Less Common Metals, 1968