REAu₃Al₇ (RE = rare earth): New ternary aluminides grown from aluminum flux

A series of ternary aluminide intermetallics with a new structure type were formed from the reaction of gold and rare-earth metals in aluminum flux. The REAu₃Al₇ structure was obtained with all rare earths RE with the exception of La and Eu. These materials crystallize in the rhombohedral space group R-3c, with unit cell parameters a=8.0922(6) Å and c=21.066(2) Å for PrAu₃Al₇ as an example. The variation in cell edges with rare-earth size is regular with the exception of the Yb analogue. The possible mixed valency indicated by this result was confirmed by magnetic susceptibility measurements. Density functional theory-based band structure calculations on YbAu₃Al₇ indicate the ytterbium f-orbitals are located just below the Fermi level, further supporting the mixed valence description of this material.