Polymerization of carbon diselenide, CSe2, at 5 kbar and sim;100thinsp;deg;C has been reported to give a metallic (CSe2)nladder polymer that superconducts near 6 K at 220 kbar pressure. Using a variety of techniques we find that the material synthesized (showing essentially the same xhyphen;ray diffraction pattern as previously published) is not (CSe2)nbut instead consists of a mixture of free, trigonal Se and an amorphous Cndash;Se polymeric composition consistent with the formula (CSe0.5)n. Interestingly, possibly as a consequence of staged reactions during synthesis, the Se phase consists of a mixture of large, aggregated crystallites (sim;600 Aring; in diameter) melting at sim;220thinsp;deg;C and nonaggregated small crystallites (sim;150ndash;250 Aring; in diameter) showing a broad melting transition with an endothermic maximum at sim;180thinsp;deg;C. Percolation of the Cndash;Se polymeric composition probably provides the high observed electrical conductivity lsqb;sgr;(300 K)ape;10ndash;20 Sthinsp;cmminus;1and sgr;(300 K)/sgr; (8 K)ape;2.5rsqb; in the presently available samples. The previously reported high pressure superconductivity is probably associated with the free Se phase in the samples, since selenium is a known superconductor in the 6 K and 220 kbar range.
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