Double Doping of BiCuSeO with Ca and Pb to Increase the Electrical Transport Properties and Reduce the Lattice Thermal Conductivity Synchronously

A series of nearly single-phase Ca-and Pb-codoped BiCuSeO bulks are fabricated via 4 min of microwave heating and 5 min of spark plasma sintering (SPS). The phase composition, microstructure, and valence state of the samples are investigated systematically, and the effects of Ca and Pb dopants being added into the samples to the alternative Bi sites on the cooperative optimization of the electrical and thermal transport properties are discussed. After codoping, the electrical conductivity and power factor of the samples are significantly improved by synchronously optimizing the carrier concentration and carrier mobility. The codoping of Ca and Pb reduces the lattice thermal conductivity, which is attributed to the introduction of high-density stacking faults and nanoprecipitates formed in the process of microwave synthesis and SPS, as well as the fluctuation of volume and mass. As a result, a maximum ZT value of 1.04 in Bi0.88Ca0.06Pb0.06CuSeO is achieved at 873 K, which is similar to 2 times larger than that of the undoped BiCuSeO. The remarkable enhancement of the thermoelectric properties combined with the simplicity and high efficiency of the synthesis method emphasizes that the preparation process will have a wide range of application prospects in the future thermoelectric field.