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

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 ( tP 80, P 4 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 .