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The movement of silver, gold, and copper in single-crystal bismuth telluride has been measured, parallel t o the cleavage planes, as a function of temperature for two current densities. At the lower current density (150 A/cm2) movement occurred always to the cathode. At the higher current density (250 A/cm2) a transition occurred from cathodic movement below about 300 "C t o bipolar movement-to both the anode and the cathode. This effect remained in evidence up t o about 400 "C with an increasing tendency t o anodic migration with increase of temperature. By about 400 OC essentially all transport occurred to the anode.The bipolar movement is considered t o be due t o the metal ions occupying two types of sites in the bismuth telluride lattice where different electrical forces are present.Similar experiments with iodine-doped bismuth telluride indicated negligible movement of iodine under co~nparable conditions.

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