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) Å and c = 4.4210(5) Å, and space group P6̄2m. The parent compound YbAuIn was also studied for comparison. YbAuIn crystallizes in the ZrNiAl structure type, hexagonal, P6̄2m space group with lattice parameters a = b = 7.7127(11) Å and c = 4.0294(8) Å. In Yb₃AuGe ₂In₃, Ge substitutes for one of the two Au positions in the ternary compound Yb₃Au₃In₃. The structure can be described as alternating [Ge₂In₃] and [Yb ₃Au] slabs that stack along the c-axis. The magnetic susceptibility data follow a modified Curie-Weiss law. The effective magnetic moment μ_eff of 0.52 μ_B/Yb atom was deduced from the Curie constant and Curie-Weiss constant of θ_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 γ term of 31 and 84 mJ/mol·K², respectively, suggesting that the ternary analog is a "light" heavy fermion compound.