Enhanced thermoelectric properties of Bi2Sr2Co2O via modulation Na+ doping and double sintering

Three groups of Bi 2– x Na x Sr 2 Co 2 O z -based samples were synthesized to investigate the combined effects of modulation Na⁺ doping and double sintering. To quantitatively analyze hole transport behavior, we introduce the modulation efficiency factor ( M ), which decouples the respective contributions of hole concentration and hole mobility to electrical conductivity. Electrical conductivity and the Seebeck coefficient are governed primarily by hole mobility and carrier effective mass, respectively. By integrating the novel fabrication processes with the quantitative metric M , the underlying transport mechanisms are elucidated, enabling a direct comparison between mobility-dominated and concentration-dominated conduction mechanisms. The proposed M parameter thus provides a quantitative metric for evaluating the effectiveness of modulation Na⁺ doping and double sintering. This work demonstrates that modulation Na⁺ doping combined with double sintering, together with the M metric, is an effective strategy for optimizing the thermoelectric performance of oxide thermoelectric materials.