Structure and chemical bonding of UAuGe

B J Gibson, R K Kremer, O Jepsen,  J D Garrett, R-D Hoffmann, R Pöttgen

UAuGe was prepared from the elements by reaction in an arc-melting furnace and subsequent annealing at about 1200 K in a water-cooled silica tube in a high-frequency furnace. UAuGe crystallizes from the melt and is also stable at 920 K. It has the hexagonal YPtAs-type structure: P63/mmc, with a = 435.26(4) pm, c = 1547.4(1) pm, V = 0.2539(1) nm3, wR2 = 0.0785, 144 F2-values, and 12 variables. The structure of UAuGe may be considered as a superstructure with a quadrupled c-axis of the well known AlB2 type. The gold and germanium atoms order on the boron positions and form two-dimensionally infinite puckered layers of Au3Ge3 hexagons with intralayer Au-Ge distances of 257 pm. Between adjacent layers the gold atoms have weak secondary Au-Au interactions with Au-Au distances of 327 pm. Ab initio calculations of the electronic band structure using the tight-binding linear muffin-tin orbital method are presented. The bonding is illustrated by valence charge density and crystal orbital Hamiltonian population plots which are compared with those of ScAuSi which has a similar structure with Au-Au interactions between the layers. The Au-Au bonding is however much weaker in UAuGe than in ScAuSi. Resistivity measurements exhibit a non-metallic temperature dependence. The increase in resistivity towards lower temperatures is uncharacteristic of intermetallic compounds, and may be fitted to a Curie-Weiss-type formula, suggesting a direct correlation to the magnetic ordering. A maximum in the resistivity is observed at T = 26(1) K.

J. Phys.: Condens. Matter 13 (2001), 3123-3137

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