Thermoelectric Power Measurements on Some Chevrel Phase Superconductors

The absolute thermoelectric power measurements on AgMo6S8, Mo6S8, pbMo6S8, SnMo6S8, SnMo6S8 were made from 4.2 to 300 k. All the compounds have positive thermoelectric power near room temperature. Mo6S8 and the compounds containing small metal ion such as Cu and Ag show a negative peak and the compounds containing large metal ion such as Pb, Sn show a positive peak in the thermopower vs. temperature graph. There seems to be a correlation between low temperature peak in the thermopower and delocalisation of the metal ion in the compound. Two mechanisms may account for the peaks in the thermopower viz. phonon drag effect and the enhancement of thermopower caused by the renormalisation of energy, velocity and relaxation time due to electron-phonon interaction. In the present case the mechanism mentioned later aoes not seem to provide an explanation for the negative peaks in the thermopower.