Suppression of magnetism and Seebeck effect in Na_0.875CoO₂ induced by Sb_Co dopants

We examined the electronic properties of Sb-doped Na_0.785CoO₂ using density functional calculations based on GGA+U formalism. We demonstrated that Sb dopants were the most stable when replacing Co ions within the complex Na_0.875CoO₂ lattice structure. We also showed that the Sb_Co dopants adopted the +5 oxidation introducing two electrons into the host Na_0.875CoO₂ compound. The newly introduced electrons recombined with holes that were borne on Co⁴⁺ sites that had been created by sodium vacancies. The elimination of Co⁴⁺ species, in turn, rendered Na_0.875(Co_0.9375Sb_0.0625)O₂ non-magnetic and diminished compound’s thermoelectric effect. Furthermore, The Sb_Co dopants tended to aggregate with the Na vacancies keeping a minimum distance. Conclusions drawn here can be generalized to other highly oxidized dopants in Na_xCoO₂ that replace a Co.