A comparative study of thermoelectric properties in (Pr,Y)Ba2Cu3O7 and PrBa2Cu3O7-Ag percolative systems

Measurements of the temperature-dependent thermoelectric power S(T) and resistivity p(7) were performed to characterize two kinds of polycrystalline systems (Pr1-xYx)Ba2CU3O7 and Ag-doped PrBa2Cu3O7, each of which exhibits percolative behaviour at a certain doping level. At room temperature, Jonker plots of the thermoelectric power against logarithm of the conductivity in both systems show a similar tendency that two different fitting lines are intercrossed at the percolation thresholds. The p(T) behaviour below 100 K in each system with low dopant content obeys the variable-range-hopping conduction. Variations of S(T) in both systems could be reconciled with the Boson-Fermion theory based on the resonating-valence-bond model with reasonable dependences of fitting parameters upon doping. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.