Realizing synergistic optimization of electrical and thermal transport properties in BiCuSeO ceramics via multi-element doping

In this study, the design of high-entropy alloys (multi-element substitution, Al▫$³⁺$▫/La▫$³⁺$▫/Sb▫$³⁺$▫/Y▫$³⁺$▫) was used to increase material entropy and improve heat scattering to further reduce thermal conductivity. Concurrently, Ca▫$²⁺$▫ ion hole doping was used to improve its electrical conductivity. Therefore, a series of Bi▫$_{0.92- x}$▫Al▫$_0.02$▫La▫$_0.02$▫Sb▫$_0.02$▫Y▫$_0.02$▫Ca▫$_x$▫CuSeO (x = 0, 0.02, 0.06, 0.10, and 0.14) ceramics was prepared using a combination of high-energy ball milling and cold isostatic pressing. The multi-element substitution of Al▫$_0.02$▫La▫$_0.02$▫Sb▫$_0.02$▫Y▫$_0.02$▫Ca▫$_0.02$▫ in the Bi site resulted in a minimum thermal conductivity of 0.35 Wm▫$^-1$▫K▫$^-1$▫, which is one-third of that of intrinsic BiCuSeO. Simultaneously, the conductivity increased up to 10–20 times that of intrinsic BiCuSeO, proportional to the amount of Ca▫$²⁺$▫ doping. Furthermore, the optimum component Bi▫$_0.82$▫Al▫$_0.02$▫La▫$_0.02$▫Sb▫$_0.02$▫Y▫$_0.02$▫Ca▫$_0.10$▫CuSeO exhibited an extremely high power factor of 568.55 μWm▫$^-1$▫K▫$^-2$▫ at 773 K, significantly higher than that of pure BiCuSeO (148.7 μWm▫$^-1$▫K▫$^-2$▫). Consequently, a peak ZT value of approximately 1.12 was achieved at 773 K, which was 4.48 times higher than that of the pristine BiCuSeO specimen (approximately 0.25). Our findings provide a novel strategy to optimize the thermoelectric properties of BiCuSeO and other materials.