The electrical- and magneto-transport properties of Rb-, Sn-, and Co-doped BiCuSeO crystals

Doped BiCuSeO is one of the promising thermoelectric oxide candidates. However, the research on doping effects on the electrical transport properties of BiCuSeO, especially in crystalline samples, is still limited. Here, we studied the transport properties of doped BiCuSeO crystals, including three types of doping species (Rb, Sn, and Co) with varying concentrations. In the case of Rb-doped BiCuSeO crystals, few percentage (≤1%) Rb-doping make BiCuSeO display metallic behavior, while high one (≥2%) displays bad-metallic behavior. Both Sn- and Co-doped BiCuSeO crystals have similar electrical evolution as Rb-doped ones. The charge carriers of all these doped BiCuSeO crystals are holes, and the increased dopant concentration decreases the hole concentrations regardless of the type of dopant species. There is negative magnetoresistance (MR) in Rb- and Sn-doped BiCuSeO at low temperature (<15 K), which is due to the breakdown of weak localization by magnetic field B, but the MR behaviors in Co-doped BiCuSeO crystals are strongly correlated with their magnetic properties. The analysis of the temperature-dependent mobility of these doped BiCuSeO crystals substantiates that at low temperatures (<50 K), electron-impurity scattering dominates, while electron–phonon scattering dominates at high temperatures (>50 K). The evolution of the above-mentioned electrical/magneto-transport properties of doped BiCuSeO can be understood as follows: the dopant compensates the Bi-deficiency in pristine BiCuSeO crystals and decreases the hole concentration and leads to the metal–Anderson-insulator transition. These results may be valuable to optimize the electrical properties of layered compounds similar to BiCuSeO.