Thermopower of tin-doped bismuth from 50 mK to 25K

The thermoelectric power of polycrystalline Bi-Sn alloys (0.02-0.16 at.%Sn) was measured in the temperature range from 50 mK up to about 25K. The disappearance of the thermoelectric voltage at the lowest temperatures correlates well with previously observed superconducting transitions in the resistance. Above 1K the thermopower is dominated by phonon drag and a large maximum is observed near 4K. With increasing Sn concentration the maximum diminishes and shifts to higher temperatures. The thermopower of a 0.02 at.%Sn alloy is particularly large and reaches 85 mu VK -1 at its maximum. Above the maximum the phonon drag contribution follows an exponential temperature dependence characteristic of a two-stage mechanism. In higher concentration alloys the exponential temperature dependence is suppressed by impurity scattering.