The combination of early rare earth metals (La- to Gd and Yb), gold, and silicon in molten aluminum results in the formation of intermetallic compounds with four related structures, forming a new homologous series: RE[AuAl 2]nAl2(AuxSi1-x) 2, with x ≈ 0.5 for most of the compound and n = 0, 1, 2, and 3. Because of the highly reducing nature of the Al flux, rare earth oxides instead of metals can also be used in these reactions. These compounds grow as large plate-like crystals and have tetragonal structure types that can be viewed as intergrowths of the BaAl4 structure and antifluorite-type AuAl 2 layers. REAuAl2Si materials form with the BaAl 4 structure type in space group I4/mmm (cell parameters for the La analogue are a = 4.322(2) Å = 10.750(4) Å, and Z = 2). REAu 2Al4Si forms in a new ordered superstructure of the KCu4S3 structure type, with space group PA/nmm and cell parameters of the La analogue of a = 6.0973(6) Å, c = 8.206(1) Å, and Z = 2. REAu3Al6Si forms in a new I4/mmm symmetry structure type with cell parameters of a = 4.2733(7) Å, c = 22.582(5) Å, and Z = 2 for RE = Eu. The end member of the series, REAu 4Al8Si, forms in space group P4/mmm with cell parameters for the Yb analogue of a = 4.2294(4) Å, c = 14.422(2) Å, and Z = 1. New intergrowth structures containing two different kinds of AuAl2 layers were also observed. The magnetic behavior of all these compounds is derived from the RE ions. Comparison of the susceptibility data for the europium compounds indicates a switch from 3-D magnetic interactions to 2-D interactions as the size of the AuAl2 layer increases. The Yb ions in YbAu 2.91Al6Si1.09 and YbAu3.86Al 8Si1.14 are divalent at high temperatures.
ASJC Scopus subject areas
- Inorganic Chemistry