Sign change of the thermoelectric power in LaCoO3
Résumé
The substitution of 1%-Ce4+ for La3+ in LaCoO 3 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 Co3+ 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 Co4+(low-spin, t 2g 5eg 0) and Co2+ (high-spin, tg 5 g 2).
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