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Scaling behavior in thermoelectric misfit cobalt oxides

P. Limelette·S. Hebert·V. Hardy·R. Fresard·Ch. Simon·A. Maignan
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Abstract

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$. 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$_0\approx$ 60 $μ$V K$^{-1}$ equal to the high temperature asymptotic value of the spin 1/2 entropy. Low temperature specific heat measurements allow us to determine an enhanced electronic part with $γ\approx$ 50 mJ (mol K$^{2}$)$^{-1}$ attesting of strong correlations. Thereby, a critical comparison between [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$, other cobaltites as well as other materials reveals a universal behavior of the thermopower low temperature slope as a function of $γ$ testifying thus 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.

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P. Limelette, S. Hebert, V. Hardy, R. Fresard, Ch. Simon, A. Maignan. 2006-08-11. Scaling behavior in thermoelectric misfit cobalt oxides. https://doi.org/10.1103/physrevlett.97.046601

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