Thermoelectric properties and power factor of YBa2Cu3O6+x with rare-earth dopants

Both the thermoelectric power and the resistivity of the oxygen deficient Y Ba2Cu3O6+x, samples were measured. The rare-earth-doped samples, such as Sm and Dy, whose magnetic moments in the +3 valence state are different, were studied. Then the power factor of the thermoelectric ability was calculate d. The power factor of the Dy-doped samples is smaller than those of the ot her samples, especially at high temperature. This smallness of the power fa ctor is the main reason why the Dy-doped samples have larger resistivity. W e try to analyze the data by the theoretical expression under the variable range hopping conduction model. The expression of the thermoelectric power could be fit for the nondoped and Sm-doped samples, except at low temperatu re. In this situation, the thermoelectric power increases as temperature in creases, and this temperature dependence is good for the thermoelectric mat erials at high temperature where the resistivity decreases with temperature increasing.