LAUSR

Oxyselenide BiCuSeO is a promising thermoelectric material in the moderate temperature range, and nanostructuring is often adopted to enhance its thermoelectric properties. In these processes, secondary phases can be either induced inadvertently via doping or intentionally processed through nanocomposites, and their effects on local thermal transport remain unresolved from the experimental point of view. In this Letter, we take Pb-doped BiCuSeO and BiCuSeO embedded with rGO (BiCuSeO-rGO) as examples, and we reveal the effect of the secondary phase on local thermal conduction via quantitative scanning thermal microscopy in combination with finite element simulation. It is found that Pb-doping effectively reduces the thermal conductivity of BiCuSeO, while the rGO secondary phase slightly increases its thermal conductivity. Good quantitative agreement is observed between our nanoscale measurement and bulk values reported in the literature. Our work thus not only offers guidance for tuning the thermal transport properties of BiCuSeO but also provides an effective method to spatially resolve heterogenous thermal conductivity at the nanoscale.