Scaling behavior in thermoelectric misfit cobalt oxides

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4](0.6)(CoO2)-Co-RS. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S-0 approximate to 60 mu V K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximate to 50 mJ (mol K-2)(-1) attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.