Structure and chemical bonding of UAuGe

J. Phys.: Condens. Matter 13 No 13 (2 April 2001) 3123-3137 
PII: S0953-8984(01)21515-X

Structure and chemical bonding of UAuGe

B J Gibson1, R K Kremer1, O Jepsen1, J D Garrett2, R-D Hoffmann3 and R Pöttgen3
1 Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
2 Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada, L8S 4M1
3 Department Chemie, Ludwig-Maximilians-Universität, Butenandtstraße 5-13 (Haus D), D-81377 München, Germany

Received 30 January 2001 

Abstract. 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.

Max-Planck Institut für Festkörperforschung;

Postfach 80 06 65   D-70506 Stuttgart