High-entropy engineering in (Sr,Ba,RE)Nb2O6-δ tungsten bronze oxides: achieving ultralow thermal conductivity and enhanced thermoelectric performance

Oxide materials are promising for thermoelectric applications due to their high thermal and chemical stability at elevated temperatures. However, their efficiency is often limited by low electrical conductivity and high thermal conductivity, stemming from simpler structures compared to complex intermetallic compounds. In this study, two novel high-entropy strontium barium niobate oxides, (Sr 0.17 Ba 0.17 La 0.17 Eu 0.17 K 0.17 Na 0.17 )Nb 2 O 6-δ and (Sr 0.17 Ba 0.17 La 0.17 Eu 0.17 K 0.17 Pb 0.17 )Nb 2 O 6-δ , were designed using high-entropy engineering. XRD confirmed the formation of a tungsten bronze structure, while SEM and EDS showed dense microstructures and uniform elemental distribution. The materials exhibit low thermal conductivity—below 1.8 W·m -1 ·K -1 from 323 to 1073 K—indicating strong thermal insulation. At 923 K, (Sr 0.17 Ba 0.17 La 0.17 Eu 0.17 K 0.17 Na 0.17 )Nb 2 O 6-δ achieves a peak power factor of 349.30 μW·m -1 ·K -2 , leading to a ZT of 0.22 at 1073 K. This improvement results from enhanced electron transport and phonon scattering enabled by high-entropy design.