Thermoelectric power factor of YBCO polycrystalline samples

A study of thermoelectric power factor, PF=S/sup 2///spl rho/, of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) samples synthesized from oxides by solid state reaction have been carried out. The Seebeck coefficient, S(T) and electrical resistivity, /spl rho/(T) were measured in the temperature range between 77 K and 300 K. The oxygen present in the samples was modified by means of an annealing process at 600/spl deg/C for different periods of time. The Seebeck coefficient is positive in whole measured temperature range and shows a linear behavior with the temperature, its magnitude increases from 30 /spl mu/V/K for the samples annealed during one hour to 1000 /spl mu/V/K for the samples annealed through 50 hours. The behavior of electrical resistivity changes from metallic to semiconducting as the annealing time is increasing. The magnitude of /spl rho/(T) increases from 10/sup -3/ /spl Omega/-cm to 10/sup -1/ /spl Omega/-cm as the annealing time increases. The thermoelectric power factor reaches values around 18 /spl mu/W/K/sup 2/cm cm in the samples annealed for 30 hours. The behavior of the transport properties suggests that the carrier density and the scattering mechanisms can be modified by decreasing the oxygen level, which open the possibility of use these kind of materials as active thermoelements.