Synergistic optimization of thermoelectric transport properties in Sb2Te3(SnTe)6 through Cd doping

Under the background of a worsening energy crisis, there is an increasing global demand for efficient and environmentally friendly energy conversion methods. Thermoelectric materials, which are capable of bidirectional conversion between thermal energy and electrical energy, show significant potential for applications in waste heat utilization and solid-state refrigeration technology. Thermoelectric materials offer innovative solutions to the current energy shortage. SnTe and PbTe share the same crystal structure and similar two-valence-band structure, but SnTe does not contain the toxic element Pb, has attracted great attention and research interest. Despite exhibiting relatively high thermoelectric performance in the medium to high-temperature range, enhancing the thermoelectric performance of SnTe near room temperature poses a challenge primarily due to its excessively high carrier concentration and low Seebeck coefficient. As the advancement of thermoelectric cooling technology continues, the performance of materials at room temperature becomes increasingly crucial. Previous studies have demonstrated that alloying with Sb2Te3 introduces a significant number of cation vacancies and dislocation defects, effectively reducing the lattice thermal conductivity of SnTe. This process also enables the modulation of the band structure, thereby increasing the effective mass, which has been demonstrated as a successful strategy for enhancing thermoelectric performance across a broad temperature range. Relevant research indicates that Sb2Te3(SnTe)(6) exhibits superior room temperature thermoelectric performance and average thermoelectric performance compared to other alloyed samples. Therefore based on the Sb2Te3 alloying approach, this study incorporates Cd doping at the Sn site to synergistically regulate the carrier concentration, density of states effective mass, and lattice thermal conductivity of Sb2Te3(SnTe)(6). Thermoelectric materials, Sb2Te3(Sn1-xCdxTe)(6) (x=0-0.08) were synthesized by vacuum melting and spark plasma sintering (SPS). The vacuum melting reactions were heated from room temperature to 1423 K over 16 hours, maintained at this temperature for 24 hours, then slowly cooled to 873 K over 6 hours, and finally cooled down to room temperature. The compounds were fully characterized by a range of techniques, including X-ray diffraction, energy dispersive spectrometer, and Hall coefficient test system, etc. The X-ray diffraction and energy dispersive spectrometer results demonstrate that Cd was successfully incorporated into Sb2Te3(SnTe)(6). The Hall coefficient test indicates that the substitution of Cd results in an obvious decrease in the carrier concentration. The Pisarenko curves calculated based on the single parabolic band model demonstrate that the effective mass increases with an increase in Cd content. The experimental results show that the effective mass of Sb2Te3(SnTe)(6) and the carrier concentration are co-optimized by doping Cd at the Sn position, and the thermoelectric transport performance of the material is significantly improved over the whole temperature range. In conclusion, this study incorporates Cd doping at the Sn site to synergistically regulate the carrier concentration, density of states effective mass, and lattice thermal conductivity of Sb2Te3(SnTe)(6). As a result, the ZT value of Sb2Te3- (Sn0.96Cd0.04Te)(6) reached 0.26 at 300 K, with an average ZT value of 0.79 in the temperature range of 323-773 K. The results indicate that SnTe-Sb2Te3 compounds exhibit significant potential for utilization in thermoelectric power generation and cooling applications.