Crystallographic Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts
Abstract:
The crystal structures of the high- and low-temperature forms of Bristol, Conn., chalcocite have been investigated with single-crystal methods. At 1250 C., high-chalcocite has lattice constants a=3.95 and c=6.75 A, and space group P63 /mmc. The sulfur atoms are arranged in hexagonal close-packing. The copper atoms are disordered. The most satisfactory approximation to the structure contains Cu atoms statistically distributed in three types of sites. Cu' is in three-fold coordination and forms of trigonal Cu-S layer. Cu" occupies the tetrahedral interstices. Cu'" is in two-fold coordination and links S atoms in neighboring Cu-S sheets. All electron density in the low-chalcocite substructure is confined to locations corresponding to positions on the 3-fold or 6-fold axes of high-chalcocite. A structure similar to that of stromeyerite, CuAgS, may be derived from that of highchalcocite by appropriate displacements of the copper atoms. The low-chalcocite structure is very likely a similar derivative structure.
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