Thermoelectric properties of PbTe-based graphene nanocomposite

PbTe is a classic thermoelectric being used commercially in interplanetary and deep space missions due its high reliability and availability for power generation, however, the low efficiency limits its broader applications. The advancement in nanostructured powder processing with low-dimensional constituents has evolved as an effective strategy for the development of high-performance materials. In this work, coarse PbTe was transformed into nanostructured material through ball milling in an inert environment. Subsequently, 1 vol% graphene was uniformly dispersed in PbTe fine powder in order to translate the favorable properties of 2D sheets to the bulk matrix. The coarse PbTe and nanostructured PbTe/graphene composite powders were consolidated by the high-frequency induction heated sintering. The temperature-dependent thermoelectric properties of the bulk samples were evaluated. The electronic transport of pure PbTe demonstrated semi-metallic conducting behavior and the composite with 1 vol% of graphene indicated somehow semiconducting trend. The Seebeck coefficient changed from positive for PbTe to negative for PbTe/graphene composite thus exhibiting transformation of majority carriers. The power factor of the composite dominated by the electrical conductivity increased at higher temperature ~ 490K from pristine PbTe. The thermal conductivity of the composite decreased substantially over the entire temperature range suggesting multiscale phonon scattering. Consequently, reduction in thermal conductivity synchronized with increase in power factor leads to enhancement of thermoelectric figure of merit of the composite above ~ 490K from pristine PbTe.