after annealing to 20 K, lnR-T ' ' was found. These films did not exhibit superconductivity as measured resistively down to the lowest temperatures attainable (T-1.5 K). The above-described behavior suggests that the Hg-Xe system exhibits a metal-nonmetal transition which occurs with a dependence on concentration and with a critical concentration close to that of continuous percolation in 3D. Beyond the percolation threshold, the systems acquire a negative TCR but are still superconductors. With further increase in Xe concentration, a regime in which the conductivity is dominated by hopping is entered. The approach to an insulating configuration beyond the percolation threshold is probably the Mott-Anderson transition of Refs. 2-4 and is accompanied by the eventual disappearance of superconductivity as determined resistively. The authors would like to thank R. Mikkelson for many helpful discussions. This work was supported by the U. S. Department of Energy under Contract No. EY-V6-S-02-1569-A002.

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after annealing to 20 K, lnR-T ' ' was found. These films did not exhibit superconductivity as measured resistively down to the lowest temperatures attainable (T-1.5 K). The above-described behavior suggests that the Hg-Xe system exhibits a metal-nonmetal transition which occurs with a dependence on concentration and with a critical concentration close to that of continuous percolation in 3D. Beyond the percolation threshold, the systems acquire a negative TCR but are still superconductors. With further increase in Xe concentration, a regime in which the conductivity is dominated by hopping is entered. The approach to an insulating configuration beyond the percolation threshold is probably the Mott-Anderson transition of Refs. 2-4 and is accompanied by the eventual disappearance of superconductivity as determined resistively. The authors would like to thank R. Mikkelson for many helpful discussions. This work was supported by the U. S. Department of Energy under Contract No. EY-V6-S-02-1569-A002.