High-temperature transport and thermoelectric properties of Ca 3Co 4− xTi xO 9

Abstract

We report the high-temperature transport and thermoelectric properties of Co-site doped Ca 3Co 4− x Ti x O 9 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 Ca 2CoO 3 sublayer; in contrast, if the relative Ti content reaches x = 0.3, the doped Ti ions may exist in both Ca 2CoO 3 and CoO 2 sublayers. As the Co ions in CoO 2 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 Ca 3Co 3.7Ti 0.3O 9 is close to 0.3 at 1000 K, suggesting that Ti doped Ca 3Co 4O 9 series are promising thermoelectric oxides for high-temperature applications.