The crystal structure of synthetic buckhornite, [Pb2BiS3][AuTe2

Abstract

Synthetic buckhornite, [Pb2BiS3][AuTe2], was grown from melts in connection with the search for high-temperature superconductive materials. Chemical analyses were performed by electron-microprobe investigations. The crystal structure was determined from 726 single-crystal X-ray reflections of a twinned crystal. The refinement gave R(F)=0.101 for 33 variable parameters. The space group is Pmmn, a=4.108(3) Å, b=12.308(9) Å, c=9.331(6) Å, Z=2. The atomic arrangement features a pronounced layer structure formed by two different sheets. (a) Planar Au[4Te]Te4 configurations are edge-connected to ribbons in [100]; they are linked by Te···Te contacts to planar nets parallel to (001). Te and Au atoms are in a distorted square arrangement. (b) Slices of (Pb,Bi)S are sandwiched between these AuTe2 layers. They form SnS-archetype layers. The present paper proves that buckhornite, [(Pb2Bi)Σ3S3] [(Te2Au)Σ3], and nagyagite, [(Pb3(Pb,Sb)3)Σ6S6][(Te,Au)3] are members of a homologous series. Both compounds have comparable Au—Te layers. However, ordering of Au and Te atoms was verified in buckhornite only. In buckhornite two (Pb,Bi)S sheets form one slice of the SnS-archetype whereas in nagyagite four (Pb,Sb)S layers form the corresponding slice with a thickness of two SnS-archetype slabs.