Sign change of the thermoelectric power in LaCoO$_\mathsf{3}$

Abstract.

The substitution of 1%-Ce^{4 +} for La^{3 +} in LaCoO₃ is found to change the sign of the Seebeck coefficient at room temperature. This demonstrates that not only holes but also electrons can be created in LaCoO₃. The result is compatible with the Heikes formula for doping levels close to the “pure” trivalent Co^{3 +} state. Nonetheless, the physical properties such as magnetic susceptibility, magnetization, thermal conductivity and resistivity are found to be asymmetric for hole and electron-doped LaCoO₃. Such a different behaviour is ascribed to the very different spin-states of Co^{4 +} (low-spin, t _2g ⁵ e _g ⁰) and Co^{2 +} (high-spin, t _2g ⁵ e _g ²).