Synergistically Optimizing Electrical and Thermal Transport Properties of BiCuSeO via a Dual-Doping Approach

The layered oxyselenide BiCuSeO system is known as one of the high-performance thermoelectric materials with intrinsically low thermal conductivity. By employing atomic, nano- to mesoscale structural optimizations, low thermal conductivity coupled with enhanced electrical transport properties can be readily achieved. Upon partial substitution of Bi³⁺ by Ca²⁺ and Pb²⁺, the thermal conductivity can be reduced to as low as 0.5 W m^-1 K^-1 at 873 K through dual-atomic point-defect scattering, while a high power factor of ≈1 × 10^-3 W cm^-1 K^-2 is realized over a broad temperature range from 300 to 873 K. The synergistically optimized power factor and intrinsically low thermal conductivity result in a high ZT value of ≈1.5 at 873 K for Bi_0.88Ca_0.06Pb_0.06CuSeO, a promising candidate for high-temperature thermoelectric applications. It is envisioned that the all-scale structural optimization is critical for optimizing the thermoelectricity of quaternary compounds. A record-high ZT value, the figure of merit, of ≈1.5 at 873 K in BiCuSeO is achieved through a Pb and Ca dual-doping approach. Synergistically, the power factor is optimized by electrical structure tuning with Pb dopants, and the thermal conductivity is reduced by phonon scattering at CaO₂ nanoclusters.