Quaternary Germanides Formed in Molten Aluminum: Tb2NiAl4Ge2 and Ce2NiAl6‐xGe4‐y (x ∼ 0.24, y ∼ 1.34)

The intermetallic phases Tb₂NiAl₄Ge₂ and Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) were synthesized in molten Al at temperatures below 1000 °C. Both compounds adopt the tetragonal space group I4/mmm with cell parameters of a= 4.1346(2) Å c = 19.3437(7) Å for Tb₂NiAl₄Ge₂ and a= 4.1951(9) Å and c = 26.524(7) Å for Ce₂NiAl_6‐xGe_4‐y. The Tb₂NiAl₄Ge₂ structure features NiAl₄Ge₂ layers separated by a double layer of rare earth ions. The Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) structure also contains the NiAl₄Ge₂ layers along with a vacancy defect PbO‐type Al_2‐xGe_2‐y layer, and is related to the Ce₂NiGa₁₀ structure type. Ordering of vacancies cause the formation of a 3ax3b superstructure in the crystal as seen by electron diffraction experiments. Tb₂NiAl₄Ge₂ exhibits Curie‐Weiss paramagnetic behavior with an antiferromagnetic transition observed at ∼20 K. Ce₂NiAl_6‐xGe_4‐y shows a much more complex magnetic behavior possibly due to temperature induced variation in the valency of the Ce atoms.