Phases in the Al-Yb-Zn system between 25 and 50 at% ytterbium

Phases YbZn1-xAlx, YbZn2-xAlx and YbZn3-xAlx were studied by electron microprobe analysis and X-ray single crystal and powder methods. The compound YbZn0.8Al0.2 crystallizes with the CsCl-type, a=3.635(2) A. Four phases were investigated by single crystal X-ray diffraction: YbZn0.996(6)Al1.004(6), MgNi2-type, P63/mmc, a=5.573(1), c=18.051(3) A, Z=8, wR2=0.040 and YbZn0.88(3)Al1.12(3), MgCu2-type, Fd3-barm, a=7.860(2) A, Z=8, wR2=0.060, both showing mixed Zn/Al occupancy; YbZn2.50(1)Al0.50(1), CeNi3-type, P63/mmc, a=5.496(1), c=17.336(2) A, Z=6, wR2=0.036 and YbZn1.92(2)Al1.08(2), PuNi3- or NbBe3-type, R3-barm, a=5.499(1), c=26.134(5) A, Z=9, wR2=0.053, where the zinc atoms are ordered in the CaCu5 segment, while share the sites with aluminium in the Laves phase segment. In the pseudobinary section YbZn2-xAlx four structures occur in sequence with increasing the electron concentration: CeCu2 or KHg2 (x=0-0.3), MgZn2 (x=0.33-0.54), MgNi2 (x=0.68-1.01) and MgCu2 (x=1.12-2). This sequence agrees with the results of first-principles calculations, already reported in the literature for other similar series. In the YbZn3-xAlx section CeNi3-type compounds occur with x=0.40-0.88 followed by PuNi3-type compounds with x=0.92-1.10. The stability ranges of these phases are related to the valence electron concentration. - Graphical abstract: In the pseudobinary section YbZn2-xAlx four structures occur in sequence on increasing the aluminium content: CeCu2 (or KHg2), MgZn2, MgNi2 and MgCu2. Volumes per atom vs. composition are reported in the figure.