Scaling of the thermoelectric power in a wide temperature range in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Nd}}_{\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_{\mathit{y}}$ (x=0–0.5): Experiment and interpretation

We report measurements of the thermopower (S) in the temperature range from ${\mathit{T}}_{\mathit{c}}$ up to 1000 K, as well as of the resistivity and the Hall coefficient for temperatures up to T=300 K of single-phase ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Nd}}_{\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{\mathit{y}}$ compounds with 0≤x≤0.5. It was found that the S(T) dependences in the normal state have three regions of different thermopower behavior. In the first region, at low temperature (T<100–220 K), the S(T) curves have a smooth maximum, which shifts to higher temperature as x increases. Then, as the temperature increases, there is an extended second region where S decreases nearly linearly with T. Finally, in the third region, at high temperature (T≳620 K), the thermopower demonstrates a temperature-independent behavior for all the investigated samples. The temperature of the crossover from the second S(T) region to the third one is unchanged with x. The results are discussed in the framework of a phenomenological band spectrum model. © 1996 The American Physical Society.