Compressibility and thermal expansion of LaNi5 and its substitutional derivatives (LaNi5−xMx; M=Mn, Al, Co)

The elastic properties of LaNi5 and related substitutional derivatives (LaNi4.6Mn0.4, LaNi4.7Al0.3, LaNi4.25Co0.75 and LaNi3.55Mn0.4Al0.3Co0.75) are investigated by means of room temperature compressibility and low-temperature thermal expansion (both studied by powder diffraction methods). Anisotropy of the compressibility and thermal expansion coefficients has been evidenced. The extent of this anisotropy changes, depending on the substituting element. A softening of the lattice accompanies also the substitution. These findings have been tentatively related to the nature and the quantity of the defects generated during hydride formation by those compounds.