Large increase in the spin entropy of thermoelectric CaCoO induced by Ni and Ce co-doping.

The effects of Ni and Ce co-doping on the spin entropy in CaCoO have been carefully studied. It is found that Ni and Ce co-doping is more effective than single rare earth element doping in improving the spin entropy of CaCoO. The largest magnetothermopower ratio value of 70 % is achieved for CaCeCoNiO, which is at least two times larger than that of the reported CaCeCoO, CaLuCoO, and CaGdCoO materials. This enhancement proves the remarkable increase in the spin entropy of Ni and Ce co-doped CaCoO. Co 2p X-ray photoemission spectroscopy shows the decrease in Co concentration induced by Ni and Ce co-doping. The reduction in Co concentration is suggested to result in the enhanced spin entropy from Co site. And coexistence of Ni and Ni provides a new hopping model for transporting spin entropy, contributing to the increase of the total spin entropy. The joint contributions from Co concentration decrease and the new hopping model, both induced by Ni and Ce co-doping, make the spin entropy increase remarkably. [ABSTRACT FROM AUTHOR]