by Oldenbourg Wissenschaftsverlag, MUnchen

Abstract. Synthetic buckhornite, [Pb2BiS,][AuTe2L was grown from melts in connection with the search for high-temperature superconductive materials. Chcmical analyses were performed by electron-microprobe investigations. The crystal structure was determined from 726 single-crys-tal X-ray reflections of a twinned crystal. The refinement gave R ( F) = 0.10 I for 33 variable parameters. The space group is Pmmn, a = 4.IOR(3) A, b = 12.308(9) A, c 9.331 (6.) A, Z 2. The atomic arrangement features a pronounced laycr structure formed by two different sheets. (a) Planar Aul4TelTe4 configurations are edge-connected to ribbons in [100]; they are linked by Te... Te contacts to planar nets parallel to (00 I). 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)DS3] [(Te2Auhi], and nagyagite, [(Pb3(Pb,Sb)3hz,Sr,]f(Te,Auh] 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 buc-khornite 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-arche-type slabs