Electron-phonon enhancement of thermopower in silver-doped superconducting Bi compounds

Resistivity, thermoelectric power (S) and critical current measurements on bulk samples of superconducting (Bi0.8Pb0.2)(2)Sr2Ca3(CU1-xAgx)(4)O12-x for different x values at small concentrations (0 less than or equal to x less than or equal to 0.02) have been carried out in the temperature range 77K - 300K. The Seebeck coefficient exhibits an enhancement above the critical temperature that increases with x. The resistivity correlates very well with the highest value of S for each sample. Although the results for S follow the universal trends found in previous works, there are some peculiarities in our data for this compound. We try to explain the S results in terms of rather conventional models. It is argued that in the copper oxides the e-p effects, usually negligible in normal metals at temperatures small compared to the Debye temperature, are significant near and above the critical temperature. A small contribution due to the phonon-drag effect is also discussed.