Liquid Ga was used as a solvent to explore the phase formation between rare-earth metals (REs), Ni, and a tetrelide (Tt = Si, Ge). The reactions were performed in excess liquid Ga at 850 °C. Two new phases of general formulas RE 0.67 Ni 2 Ga 5-x Tt x and RE 0.67 Ni 2 Ga 6-x Tt x were found and structurally characterized. The Co analogues of the latter RE 0.67 Co 2 Ga 6-x Ge x (RE = Y, Gd) were also prepared. Single-crystal X-ray data: The first group of compounds RE 0.67 Ni 2 Ga 5-x Tt x crystallizes in the hexagonal space group P6 3 /mmc with a structure related to the RE 2-x Pt 4 Ga 8+y type (Sm 0.53 Ni 2 Ga 5-x Ge x , a = 4.1748(7) A, c = 16.007(4) A, V = 241.61(8) A 3 , Z = 2; Y 0.59 Ni 2 Ga 5-x Ge x , a = 4.1344(11) A, c = 15.887(6) A, V = 235.18(12) A 3 , Z = 2; Tb 0.67 Ni 2 Ga 5-x Si x , a = 4.1415(11) A, c = 15.843(6) A, V = 235.33(12) A 3 , Z = 2; Ho 0,67 Ni 2 Ga 5-x Ge x , a = 4.1491(4) A, c = 15.877(2) A, V = 236.71(5) A 3 , Z = 2). The second group RE 0.67 Ni 2 Ga 6-x Tt x crystallizes inP6m2 (Gd 0.67 Ni 2 Ga 6-x Ge x , a = 4.1856(10) A, c = 9.167(3) A, V = 139.08(7) A 3 , Z = 1; Sm 0.67 Ni 2 Ga 6-x Si x , a = 4.1976(8) A, c = 9.159(3) A, V = 139.76(5) A 3 , Z = 1) in a structure related to the ErNi 3 Al 9 structure type with disorder in the RE-Ga plane. Dy 0.67 Ni 2 Ga 6-x Ge x crystallizes in space group P31c (a = 7.2536(8) A, c = 18.308(3) A, V = 834.21(2) A 3 , Z = 6) with partial disorder in the RE-Ga plane. The structures of these two groups of compounds are related to each other and contain similar building motifs, namely Ga n [NiGa 2-x/2 Ge x/2 ] 2 slabs and RE 0.67 Ga monatomic layers which alternate along the c-direction, forming a 3D structure. The parameter x and the position of the tetrelide in the structure were determined by single-crystal neutron diffraction. Complete or partial disorder of the RE and Ga atoms is observed in the RE-Ga plane. The origin of the disorder lies in the extensive and random stacking faults of ordered RE-Ga planes, which apparently slide easily in the ab plane and create an averaged disordered picture. Electrical conductivity and thermopower measurements indicate that these compounds are metallic conductors. The magnetic measurements show antiferromagnetic ordering at ∼3-4 K and Curie-Weiss behavior at higher temperatures with the values of μ eff close to those of RE 3+ free ions. Strong 2-fold crystal field anisotropy is observed for the heavy RE analogues. The anisotropy constants K 2 para calculated from the Weiss constant anisotropy for heavy RE analogues are reported.
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