Enhanced thermoelectric performance of Sr_0.875La_0.1TiO_3-δ based composites through Bi-rich inclusions in internal and external reduction environments

The electrical transport performance of bulk SrTiO₃ thermoelectric materials can be optimized by incorporating uniformly dispersed conductive inclusions. Herein, the impact of Bi₂O₃ addition on the thermoelectric properties of La-doped strontium titanate composite nano Ti powder (Sr_0.875La_0.1TiO_3-δ/20 wt% Ti) has been examined. During the sintering process, Bi₂O₃ gradually transforms into a liquid phase to facilitate Redox reactions with nano Ti and mass transfer, followed by reduction and transformation into Bi–Bi₂O₃ particles that precipitate at grain boundaries. The presence of nanoscale Bi-rich phases reduces carrier transport barriers at grain boundaries and enhances phonon relaxation time associated with grain boundary scattering. Ultimately, the sample containing 10 wt% bismuth oxide exhibits the lowest lattice thermal conductivity and the highest weighted mobility. This led to a maximum power factor of 498 μW/mK² at 873 K and a maximum ZT value of 0.188 at 1073 K. This study presents a novel approach to decouple electroacoustic transport through the utilization of Redox reactions between multiple phases, offering valuable insights for the development of high-performance thermoelectric oxide composites.