New structure type in the mixed-valent compound YbCu₄Ga₈

Abstract

The new compound YbCu₄Ga₈ was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu₄Ga₈ crystallizes in the CeMn₄Al₈ structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu₄Ga₈ is composed of pseudo-Frank–Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu₄Ga₈ investigated in the temperature range 2–300 K showed Curie–Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.