High-temperature transport and thermoelectric properties of Ca3Co4−xTixO9

We report the high-temperature transport and thermoelectric properties of Co-site doped Ca3Co4−xTixO9 system. The results reveal that both resistivity and thermopower increase monotonously with Ti doping. When the relative Ti content is not more than x = 0.2, the substitution takes place in Ca2CoO3 sublayer; in contrast, if the relative Ti content reaches x = 0.3, the doped Ti ions may exist in both Ca2CoO3 and CoO2 sublayers. As the Co ions in CoO2 layer are substituted, the transport mechanism of the system varies, and the electronic correlation is pronounced enhanced. These changes induce a noticeable increase in thermopower. The figure of merit ZT value of Ca3Co3.7Ti0.3O9 is close to 0.3 at 1000 K, suggesting that Ti doped Ca3Co4O9 series are promising thermoelectric oxides for high-temperature applications.