The ternary Laves phase Nb(Ni1−xAlx)2 with MgZn2 -type

Alloys with nominal composition Nb(Ni1−xAlx)2 (xAl=0.15, 0.23, 0.30, 0.38, 0.46, 0.54, 0.62, 0.69, 0.77, 0.85) were investigated by means of X-ray powder and single crystal diffraction, optical microscopy, electron probe microanalysis (EPMA) concentrating on structural details of the C14 MgZn2-type Laves phase. Rietveld refinements of X-ray powder data ( 0.23 < x Al < 0.77 ) revealed that Nb atoms fully occupy the 4f sites, whereas Ni and Al atoms share 6h and 2a sites in a random fashion. Single crystal refinement for Nb(Ni0.54Al0.46)2 confirmed structure type and atom order in line with results from powder diffraction. The characteristic site preferences throughout the series of alloys serve as a basis for the interpretation of the non-linear dependence of unit cell parameters with Al content.