Power factor enhancement in NaxCoO2 doped by Bi

Abstract Polycrystalline materials of Na 0.74− x Bi x CoO 2 (0 ⩽ x ⩽ 0.3) have been prepared by combining solid state reaction with sintering process. The effects of partial substitution of Bi for Na-site on the thermoelectric performance of Na 0.74 CoO 2 have been investigated. The optimal doping level was achieved when x = 0.15, at which the power factor is 3.6 times as large as that of the non-substituted one. The results indicate that the electrical conductivity and Seebeck coefficient of Bi-doped sample ( x = 0.15) increase dramatically (two times and 24.6%, respectively) compared with the free-doped sample, which may be attributed to the adjustment of crystal structure and carrier mobility.