Figure of merit factor of ceramic superconductors

We report on the temperature (20-300 K) dependence of the thermopower S(T) thermal conductivity κ(T) and electrical resistivity ρ(T) of several HgBaCaCuO (1223), BiSrCaCuO (2212) and DyBaCuO (123) polycrystalline superconductors. We present some discussion on the precision and the originality of the measurement methods which are especially geared toward the electrical resistivity and simultaneously the thermopower and the thermal conductivity as a function of temperature. The figure of merit z(T) = S2(T)/[κ(T)/σ(T)] of these superconducting materials is calculated and compared. The results show that at room temperature z(T) is 103 - 104 smaller than for n-and p-type semiconductors materials used in present refrigeration devices. Nevertheless below the superconductivity critical temperature the superconductor materials can replace the p-type semiconductor in the thermoelectric refrigerator devices. This is shown by discussing the figure of merit z of such a composite thermoelectric refrigerator made of a superconductor and a n- type semiconductor.