Structure andchemical bonding of UAuGe

Abstract

UAuGe was prepared from the elements by reaction in an arc-meltingfurnace and subsequent annealing at about 1200 K in a water-cooledsilica tube in a high-frequency furnace. UAuGe crystallizes fromthe 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 12variables. The structure of UAuGe may be considered as asuperstructure with a quadrupled c-axis of the well knownAlB2 type. The gold and germanium atoms order on the boronpositions and form two-dimensionally infinite puckered layers ofAu3Ge3 hexagons with intralayer Au-Ge distances of 257 pm.Between adjacent layers the gold atoms have weak secondary Au-Auinteractions with Au-Au distances of 327 pm. Ab initiocalculations of the electronic band structure using thetight-binding linear muffin-tin orbital method are presented. Thebonding is illustrated by valence charge density and crystal orbitalHamiltonian population plots which are compared with those ofScAuSi which has a similar structure with Au-Au interactionsbetween the layers. The Au-Au bonding is however much weaker inUAuGe than in ScAuSi. Resistivity measurements exhibit anon-metallic temperature dependence. The increase in resistivitytowards lower temperatures is uncharacteristic of intermetalliccompounds, and may be fitted to a Curie-Weiss-type formula,suggesting a direct correlation to the magnetic ordering. A maximumin the resistivity is observed at T = 26(1) K.