Enhanced high-temperature thermoelectric performance of the n-type WO2.72 Ceramics: reduced lattice thermal conductivity via microstructure engineering

This study presents a strategy to improve thermoelectric properties of substoichiometric pentagonal−columnar WO_2.72 oxides through microstructure engineering via the incorporation of Ta₂O₅ inclusions as a secondary phase. A series of xTa₂O₅WO_2.72 oxides (x = 0–0.15) were synthesized via solid−state reaction in inert atmosphere. XRD and SEM analyses confirm the coexistence of Ta₂O₅ segregations within the WO_2.72 crystal lattice structure without chemical reaction and reveal a nanorod−like grain morphology in the material. These structural modifications introduce significant phonon−scattering sites, reducing total thermal conductivity by half. Simultaneously, the Seebeck coefficient magnitude increases by 43% compared to the pristine phase, sufficient to compensate for the elevation in the resistivity caused by the introduction of the secondary−phase inclusions, thereby maintaining competitive power factors above 1000 K. A peak zT of 0.13 at 1073 K is achieved for x = 0.15, nearly tripling the figure of pristine materials. The results highlight the effectiveness of microstructure−driven strategies for decoupling thermal and electronic transport in oxide thermoelectric.