Single crystal investigation of the YbAl2 compound

Abstract

A sample of nominal composition Yb33,3Al66,7 was synthesized from high-purity elements (Yb ≥ 98.9 wt.% and Al ≥ 99.999 wt.%) by arc-melting under a purified argon atmosphere, using Ti as a getter and a tungsten electrode. To achieve high efficiency of the interaction between the components, the sample was melted twice. The ingot was annealed at 500°C in an evacuated quartz ampoule for 720 h and subsequently quenched in cold water. The weight loss during the preparation of the sample was less than 1 % of the total mass, which was 2 g. The chemical composition of the selected crystals was checked with a field-emission scanning electron microscope (FEINovaNanoSEM 230) equipped with an EDS analyzer.
 Laue and rotation diffraction patterns of selected single crystals showed cubic symmetry. Integrated intensities measured with graphite-monochromatized Мо Kα radiation (l = 0.71073 Å) on an Xcalibur Atlas CCD diffractometer confirmed the cubic lattice. The structure type MgCu2 was assigned and the structure was refined using the program SHELXL (full-matrix least-squares refinement on F2)] with anisotropic displacement parameters for all of the atoms: Pearson symbol cF24, space group Fd-3m, a = 7.7011(4) Å, V = 456.73(7) Å3, Z = 8, R = 0.0261, Rw = 0.0726 for 42 reflections.
 It is well-known that the trivalent state is usual one for the rare earth metals. The dependence of the mean atomic volume of the RAl2 binary showed of the so-called “valence” fluctuation state for Eu and Yb.