Thermoelectric power and thermal conduction studies on the Nd substituted BPSCCO (2234) superconductors

In this study, we have carried out thermoelectric power (S-T) and thermal conductivity (κ-T) measurements from room temperature down to 15 K on Bi1.7Pb0.3−xNdxSr2Ca3Cu4O12+y samples, where 0.0 ⩽ x ⩽ 0.1. The thermoelectric powers, S(T), of the samples have both negative (at high T) and positive values (at low T), and are found to increase with decreasing temperature, reaching maxima (peaks) around their Tc values and to drop rapidly to zero below Tc. The magnitude of the peaks decreases with increasing Nd-content. The results obtained have been analyzed in terms of the “two-band model with linear T-term” and “Xin's two-band model”. A very good agreement between the first model and our thermoelectric power data is obtained, but the fit to the second model is poor. The fittings to the models indicate that while the electrons are effective at higher temperatures, the holes become dominant at lower temperatures, the number of holes and the Fermi energies decrease with increasing Nd-content. Nd substitution also has a considerable effect on the thermal conductivity, κ. A broad maximum is obtained on κ versus T plot, just below the Tc value of each sample. However, the peaks decrease in intensity and also broaden with increasing Nd concentration. This behavior is believed to be due to the scattering of the carriers.