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

Abstract

The intermetallic compound Yb₂AuGe₃ was synthesized from indium flux. Yb₂AuGe₃ crystallizes in the orthorhombic Ca₂AgSi₃-type structure which is an ordered superstructure of the AlB₂ 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 Yb₂AuGe₃ 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. Yb₂AuGe₃ is metallic, and at low temperature the resistivity varies as T², indicating possible Fermi liquid behavior. Heat capacity measurements suggest that Yb₂AuGe₃ is possibly a moderate heavy fermion system.