Optimization of the spin entropy by incorporating magnetic ion in a misfit-layered calcium cobaltite

Effects of (Lu, Ni) co-doping on spin entropy of Ca3Co4O9+δ have been investigated. Results of this study show that (Lu, Ni) co-doping can be more effective than single Lu doping for optimizing the spin entropy of Ca3Co4O9+δ. X-ray photo-emission spectroscopy confirms a reduction in Co4+ concentration, which leads to enhanced spin entropy from Co sites. The magnetic ions of Ni with unpaired 3d electrons can produce extra spin entropy through a new hopping model, thereby contributing to an increase in total spin entropy. Incorporating magnetic ions is an effective way to optimize the spin entropy of thermoelectric materials. This study opens a new way to broaden and design prospective thermoelectric materials.