Improving bulk Ca ₃ Co ₄ O ₉ thermoelectric materials through Zr doping

Ca3Co4−xZrxOy polycrystalline ceramics with small Zr substitution have been prepared through the classical solid-state method. X-ray diffraction data have shown that all samples are composed only of Ca3Co4O9 and Ca3Co2O6 phases. Moreover, by increasing Zr substitution up to 0.07, Ca3Co2O6 phase content is decreased. Density measurements have revealed that all samples are very similar, with values around 74% of the theoretical density. Electrical resistivity is decreased in Zr-doped samples, with respect to the pure samples, while Seebeck coefficient is unchanged. Both factors lead to power factor values around 0.33 mW K−2 m−1 at 800°C in 0.07 Zr-doped samples, which are about 65% higher than those obtained for the undoped samples.