ИСТИНА

Two polymorphic modifications of Yb2PdGe6 were previously identified by means of single crystal X-ray diffraction technique [1,2], but neither X-ray nor neutron diffraction experiments were performed so far on polycrystalline samples, which would be verify the proposed structural models on bulk material. In the present work, a polycrystalline sample of nominal composition Yb22Pd11Ge67 (at. %) was prepared via 25 arc-melting stages with adding excess of Yb at each stage.The crystal structure of Yb2PdGe6 was studied by X-ray powder diffraction at room temperature using the STOE STADI P transmission diffractometer (monochromatized CuKα1 – radiation (λ= 1.54056 Å), 6° < 2θ < 106°, linear position-sensitive detector. In both as-cast and annealed (730 °C, 30 days) alloys the title compound is isotypic to the polymorphic high or low temperature modification reported by Fornasini et al. [1]: space group Cmca (No.64), a = 8.1192(6), b = 7.9579(5), c = 21.736(2) Å, V = 1404.4(2) Å3, Z = 8. The crystal structure can be presented as a sequence of AlB2, BaAl4 and distorted α-Po type slabs along the c direction. Rietveld refinement of the X-ray data revealed a nearly single phase specimen. Electron probe microanalysis indicated a main matrix of Yb22Pd11Ge67 (at. %) and the presence of a minor amount of Yb2O3. The low-temperature physical properties of the annealed sample of Yb2PdGe6 were studied by means of magnetisation and electrical resistivity measurements. The compound was found to exhibit valence fluctuations due to unstable 4f-shell of ytterbium ions. Analysis of the magnetic susceptibility data in terms of the Sales-Wohlleben approach [3] yielded the characteristic temperature scale in the system Tsf ≈ 340 K, and the average effective Yb-ion valence of about +2.4 at 400 K.