A novel high-entropy oxide Sr0.7Ba0.3(Nb0.2Hf0.2Ta0.2Zr0.2Ti0.2)2O6-δ: Achieving ultralow thermal conductivity through highly disordered B-site cations

As promising thermoelectric materials, high-entropy oxides (HEOs) have garnered considerable research interest. In this work, a novel tungsten bronze-type niobate ceramic, Sr 0.7 Ba 0.3 (Nb 0.2 Hf 0.2 Ta 0.2 Zr 0.2 Ti 0.2 ) 2 O 6-δ , was successfully synthesized via a conventional solid-state reaction. Comprehensive characterization using XRD, SEM-EDS, and TEM confirmed the formation of a high-entropy material with multiple cations incorporated at the B-site, inducing pronounced local cationic disorder. This high-entropy design at the B-site introduces severe lattice distortion and mass/stress field fluctuations, which significantly enhance phonon scattering and lead to an ultra-low total thermal conductivity. After 20 h of reduction treatment, the sample achieved a remarkably low thermal conductivity of 0.59 W·m −1 ·K −1 at 323 K and 1.29 W·m −1 ·K −1 at 1073 K, ranking among the lowest values reported to date for strontium barium niobate-based thermoelectric materials. This study shows that B-site high-entropy engineering effectively suppresses lattice thermal conductivity in complex oxides, offering a promising route for next-generation high-temperature n-type thermoelectrics.