Yb3AuGe2In3: An Ordered Variant of the YbAuIn Structure Exhibiting Mixed-Valent Yb Behavior

Yb3AuGe2In3 was obtained as large single crystals in high yield from reactions run in liquid indium. Single crystal X-ray diffraction data show that Yb3AuGe2In3 is an ordered variant of YbAuIn with lattice constants, a = b = 7.3153(8) angstrom and c = 4.4210(5) angstrom, and space group P (6) over bar 2m. The parent compound YbAuIn was also studied for comparison. YbAuIn crystallizes in the ZrNiAl structure type, hexagonal, P (6) over bar 2m space group with lattice parameters a = b = 7.7127(11) angstrom and c = 4.0294(8) angstrom. In Yb3AuGe2In3, Ge substitutes for one of the two Au positions in the ternary compound Yb3Au3In3. The structure can be described as alternating [Ge2In3] and [Yb3Au] slabs that stack along the c-axis. The magnetic susceptibility data follow a modified Curie-Weiss law. The effective magnetic moment mu(eff) of 0.52 mu(B)/Yb atom was deduced from the Curie constant and Curie-Weiss constant of theta(p) = -1.5 K indicating antiferromagnetic interactions in Yb3AuGe2In3. X-ray absorption near edge spectroscopy (XANES) measurements indicate intermediate valency for Yb in both compounds. The metallic nature of both compounds was confirmed by the resistivity measurements. Specific heat data for Yb3AuGe2In3 and YbAuIn give an electronic gamma term of 31 and 84 mJ/mol.K-2, respectively, suggesting that the ternary analog is a "light" heavy fermion compound.