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Order/disorder in YbNi1±xGa2∓x (x ≤ 0.08): Crystal structure, thermal expansion and magnetic properties

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Title:	Order/disorder in YbNi1±xGa2∓x (x ≤ 0.08): Crystal structure, thermal expansion and magnetic properties
Authors:	Vasylechko, L.^1,2 crystal-lov@polynet.lviv.ua, Burkhardt, U.¹, Schnelle, W.¹, Borrmann, H.¹, Haarmann, F.³, Senyshyn, A.⁴, Trots, D.⁵, Hiebl, K.⁶, Grin, Yu.¹ grin@cpfs.mpg.de
Source:	Solid State Sciences. Jun2012, Vol. 14 Issue 6, p746-760. 15p.
Subjects:	Crystal structure, Chemical systems, Ytterbium compounds, Magnetic properties of metals, Thermal expansion, Ternary phase diagrams, Fusion (Phase transformation), Annealing of metals
Abstract:	Abstract: The ternary phase (x ≤ 0.08) has been synthesised from the elements by high-frequency melting in argon atmosphere with subsequent annealing at 600 °C or 800 °C. From X-ray powder and single crystal diffraction investigations the phase is found to be isotypic with MgCuAl2: space group Cmcm, Z = 4, a = 4.0987–4.1147 Å, b = 9.8516–9.8620 Å, c = 6.5995–6.5916 Å for the specimens annealed at 800 °C. The quantum chemical analysis of atomic interactions in YbNiGa2 shows Ga and Ni forming a network polyanion with covalent bonds, while ytterbium cations are located within the cavities of the polyanion. From the magnetic susceptibility data and L III XAS spectra, the 4f 13 electronic configuration of ytterbium (Yb3+) was established in samples with nickel excess (comparing to x = 0), whereas an additional small contribution of the 4f 14 configuration is found for compositions with the gallium excess. No change in the ytterbium valence state was detected down to 5 K. In situ low- and high-temperature powder diffraction investigations applying both X-ray synchrotron radiation and neutrons revealed no change in structure within the broad temperature range 3.4–1173 K. Both synchrotron and neutron diffraction data show smooth, but strongly anisotropic variation of lattice parameters below 200 K: the thermal contraction ratio in [100], [010] and [001] directions is 4.5:3.2:1. The temperature dependence of atomic displacement parameters indicates a certain amount of static disorder for all atomic species in the crystal. At least two distinct sites with varying charge distributions in the vicinity of the Ga atoms are confirmed by 69,71Ga NMR spectroscopy. [Copyright &y& Elsevier]
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Database:	Engineering Source

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Abstract:	Abstract: The ternary phase (x ≤ 0.08) has been synthesised from the elements by high-frequency melting in argon atmosphere with subsequent annealing at 600 °C or 800 °C. From X-ray powder and single crystal diffraction investigations the phase is found to be isotypic with MgCuAl2: space group Cmcm, Z = 4, a = 4.0987–4.1147 Å, b = 9.8516–9.8620 Å, c = 6.5995–6.5916 Å for the specimens annealed at 800 °C. The quantum chemical analysis of atomic interactions in YbNiGa2 shows Ga and Ni forming a network polyanion with covalent bonds, while ytterbium cations are located within the cavities of the polyanion. From the magnetic susceptibility data and L III XAS spectra, the 4f 13 electronic configuration of ytterbium (Yb3+) was established in samples with nickel excess (comparing to x = 0), whereas an additional small contribution of the 4f 14 configuration is found for compositions with the gallium excess. No change in the ytterbium valence state was detected down to 5 K. In situ low- and high-temperature powder diffraction investigations applying both X-ray synchrotron radiation and neutrons revealed no change in structure within the broad temperature range 3.4–1173 K. Both synchrotron and neutron diffraction data show smooth, but strongly anisotropic variation of lattice parameters below 200 K: the thermal contraction ratio in [100], [010] and [001] directions is 4.5:3.2:1. The temperature dependence of atomic displacement parameters indicates a certain amount of static disorder for all atomic species in the crystal. At least two distinct sites with varying charge distributions in the vicinity of the Ga atoms are confirmed by 69,71Ga NMR spectroscopy. [Copyright &y& Elsevier]
ISSN:	12932558
DOI:	10.1016/j.solidstatesciences.2012.03.029