Quaternary Germanides Formed in Molten Aluminum: Tb2NiAl4Ge2 and Ce2NiAl6-xGe4-y (x ∼ 0.24, y ∼ 1.34)Dedicated to Professor Welf Bronger on the Occasion of his 70th Birthday

The intermetallic phases Tb2NiAl4Ge2 and Ce2NiAl6-xGe4-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 Ce2NiAl6-xGe4-y. The Tb2NiAl4Ge2 structure features NiAl4Ge2 layers separated by a double layer of rare earth ions. The Ce2NiAl6-xGe4-y (x ∼ 0.24, y ∼ 1.34) structure also contains the NiAl4Ge2 layers along with a vacancy defect PbO-type Al2-xGe2-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. Ce2NiAl6-xGe4-y shows a much more complex magnetic behavior possibly due to temperature induced variation in the valency of the Ce atoms.