Site Occupancies in the Battery Electrode Material LaNi_3.55Mn_0.4Al_0.3Co_0.75 as Determined by Multiwavelength Synchrotron Powder Diffraction

The battery electrode material LaNi_3.55Mn_0.4Al_0.3Co_0.75 is a substitutional derivative of LaNi₅ in which La occupies site 1(a), and Ni, Mn, Al and Co sites 2(c) and 3(g) of space group P6/mmm. The distribution of the substituting elements Mn, Al and Co on the two latter sites was determined from synchrotron powder diffraction experiments by using the diffraction contrast produced by anomalous dispersion effects. The results of joint Rietveld refinement on three patterns collected close to the K edges of Ni, Co and Mn and on one pattern collected away from these edges showed that Al and Mn occupy almost exclusively site 3(g), while Co is distributed over sites 2(c) and 3(g) with a slight preference for site 3(g).