Superconducting YAu(3)Si and Antiferromagnetic GdAu(3)Si with an Interpenetrating Framework Structure Built from 16-Atom Polyhedra

[Image: see text] Investigations of reaction mixtures RE(x)(Au(0.79)Si(0.21))(100–x) (RE = Y and Gd) yielded the compounds REAu(3)Si which adopt a new structure type, referred to as GdAu(3)Si structure (tP80, P4(2)/mnm, Z = 16, a = 12.8244(6)/12.7702(2) Å, and c = 9.0883(8)/9.0456(2) Å for GdAu(3)Si/YAu(3)Si, respectively). REAu(3)Si was afforded as millimeter-sized faceted crystal specimens from solution growth employing melts with composition RE(18)(Au(0.79)Si(0.21))(82). In the GdAu(3)Si structure, the Au and Si atoms are strictly ordered and form a framework built of corner-connected, Si-centered, trigonal prismatic units SiAu(6). RE atoms distribute on 3 crystallographically different sites and each attain a 16-atom coordination by 12 Au and 4 Si atoms. These 16-atom polyhedra commonly fill the space of the unit cell. The physical properties of REAu(3)Si were investigated by heat capacity, electrical resistivity, and magnetometry techniques and are discussed in the light of theoretical predictions. YAu(3)Si exhibits superconductivity around 1 K, whereas GdAu(3)Si shows a complex magnetic ordering, likely related to frustrated antiferromagnets exhibiting chiral spin textures. GdAu(3)Si-type phases with interesting magnetic and transport properties may exist in an extended range of ternary RE–Au–Si systems, similar to the compositionally adjacent cubic 1/1 approximants RE(Au,Si)(∼6).