Metallic Yb2AuGe3: an ordered superstructure in the AlB2-type family with mixed-valent Yb and a high-temperature phase transition.

The intermetallic compound Yb(2)AuGe(3) was synthesized from indium flux. Yb(2)AuGe(3) crystallizes in the orthorhombic Ca(2)AgSi(3)-type structure which is an ordered superstructure of the AlB(2) structure type. The structure was refined in the Fmmm space group with lattice parameters a = 8.5124(17) Å, b = 14.730(3) Å, c = 8.4995(17) Å. Temperature-dependent powder X-ray diffraction studies show that Yb(2)AuGe(3) undergoes a phase transition from orthorhombic to hexagonal upon heating above 773 K. The compound shows weak paramagnetism that derives from a combination of Curie and Pauli paramagnetism with a magnetic moment value of 0.33(2) µ(B)/Yb atom. Magnetic ordering was not observed down to 2 K. Yb(2)AuGe(3) is metallic, and at low temperature the resistivity varies as T(2), indicating possible Fermi liquid behavior. Heat capacity measurements suggest that Yb(2)AuGe(3) is possibly a moderate heavy fermion system.