Bi doping enhances the thermoelectric properties of tetragonal tungsten bronze Sr0.7Ba0.3Nb2O6 ceramics

Strontium barium niobate (SBN) with a tetragonal tungsten bronze structure is a promising n -type oxide thermoelectric material, but its high intrinsic thermal conductivity limits further improvement of the thermoelectric figure of merit (ZT). In this study, A-site Bi-doped (Sr 0.7 Ba 0.3 ) 1-x Bi x Nb 2 O 6 (x=0.00, 0.05, 0.10, 0.15) ceramics were synthesized by a solid-state reaction method, and the effect of Bi doping on the microstructure and thermoelectric transport properties was systematically investigated. The results show that Bi 3+ ions are successfully incorporated into the A-sites of the SBN lattice, inducing local lattice distortions and introducing oxygen vacancies. TEM observations reveal high-density dislocations and lattice distortions. Electrical transport analysis indicates that Bi doping significantly increases the carrier concentration and reduces the carrier activation energy by introducing oxygen vacancies, which suppresses the contribution of small polaron hopping conduction and promotes band transport, thereby markedly decreasing the electrical resistivity. Meanwhile, the 6s 2 lone-pair electrons of Bi 3+ modulate the band structure, maintaining a considerable Seebeck coefficient at a relatively high carrier concentration. The x = 0.10 sample achieves a high-power factor of 410.4 μW·m −1 ·K −2 at 1073 K. In terms of thermal transport, the mass fluctuations, lattice distortions, and dislocation defects introduced by Bi doping constitute multiple phonon scattering centers, effectively reducing the lattice thermal conductivity. Finally, benefiting from the synergistic optimization of electrical and thermal transport, the x = 0.10 sample attains a maximum ZT of 0.24 at 1073 K. This study confirms that Bi doping is an effective strategy to enhance the thermoelectric performance of SBN-based materials and provides a new route for developing high-performance oxide thermoelectric materials.