Magnetic, transport, and thermal properties of Yb2T3X9 compounds (T=Rh, Ir; X=Al, Ga)

The low-temperature properties of a family of ytterbium-based compounds wit h the composition Yb2T3X9 (T = Rh, Ir; X = Al, Ga) are studied by means of magnetic susceptibility, electrical resistivity, thermoelectric power, and specific-heat C-P measurements. Yb2Rh3Al9 and Yb2Ir3Al9 show the typical pr operties of heavy-fermion antiferromagnets, namely they order at T-N = 3.5 K and T,= 5.5 K, respectively, their C-P/T data extrapolate to y(0) = 230 m J/mol Yb K-2 below 0.5 K, and their entropy gain at T-N reaches 0.6R ln 2 o nly. The transport data show evidence of low-lying crystal-electric-field l evels separated by Delta(CEF) similar or equal to 30 K from che ground-slat e doublet. On the contrary, Yb2Rh3Ga9 and Yb2Ir3Ga9 show mixed-valent behav ior, as observed in most Yb-based intermetallics. The effect of the Ligands on the ground-state properties is discussed and compared with other lantha nide- and actinide-based isostructural R2T3X9 homologues.