Flux synthesis, structure and physical properties of new pseudo-binary REAl_3-xGe_x compounds

New compounds in the system RE-Al-Ge (RE = Tb, Gd, Ho) were prepared in molten aluminum. Large, (up to 5 mm) single crystals of new pseudo-binary phases GdAl_3-xGe_x, (x = 0.1), TbAl_3-xGe_x, (x = 0.3), and HoAl_3-xGe_x, (x = 0.2) were recovered in high yield. The crystal structures were refined by single crystal X-ray diffraction techniques, and found to vary as a function of rare-earth element. Thus, GdAl_3-xGe_x crystallizes in the Ni₃Sn structure type (P6₃/mmc) of GdAl₃. For the TbAl_3-xGe_x the BaPb₃ structure type (R-3m) is adopted, as it is for TbAl₃. In the case of HoAl_3-xGe_x, the structure type of HoAl₃ is not stabilized, and the compound crystallizes in the BaPb₃ structure (R-3m). Crystal data: GdAl_3-xGe_x a = 6.3115(4) angstroms, c = 4.6052(4) angstroms, V = 158.87(2) angstroms³, P6₃/mmc (No. 194, Z = 2); TbAl_3-xGe_x a = 6.1956(9) angstroms, c = 21.025(4) angstroms, V = 698.9(2) angstroms³, R-3m (No. 166, Z = 9); HoAl_3-xGe_x a = 6.1579(10) angstroms, c = 21.062(5) angstroms, V = 691.7(2) angstroms³, R-3m (No. 166, Z = 9). Charge transport properties indicate that these materials are good metallic conductors. At low temperatures they order antiferromagnetically, whereas above approximately 50 K they are Curie-Weiss paramagnets. The temperature of maximum magnetic susceptibility (T_max) is 5.93 K, 18.8 K, and 24.0 K for HoAl_2.8Ge_0.2, TbAl_2.7Ge_0.3, and GdAl_2.9Ge_0.1 respectively.