Current Happenings

Projects: PbTe

The research interests lie in developing the next generation of Thermoelectric (TE) Materials and pursuing a comprehensive understanding regarding the basic science of the energy conversion related thermal and electrical transport properties. The global demand for affordable, renewable and clean energy resources to reduce our dependence on carbon based fossil energy leads to important regimes of research, among which the thermoelectrics has a noticeable place. Heat from abundant sources such as solar heat, geothermal heat, exhaustion of the automobiles can be directly converted into clean electricity via thermoelectric (TE) devices that are all solid-state, quite, compact and maintenance-free. However, the efficiency of the state-of-the art TE generator, about 7-8 %, is still relatively low as compared to other peer energy conversion techniques such as solar energy, wind power and nuclear energy. The challenge is in the material.

One rapidly emerging field in the current study of thermoelectric materials is the concept of nanocomposite thermoelectric (TE) materials.  A nanocomposite TE material is one in which nanoscaled structures are incorporated into the matrix of a conventional bulk TE material in the hope of reaching a compromise between the outstanding TE properties of the nanoscaled structures and the proven performance of the bulk TE materials. As suggested both theoretically and experimentally, the superior TE properties of the nanostructures to its bulk counterpart are due to the size-effect, dimensionality effect and grain-boundary scattering of phonons and charge carriers. Only the first two are intrinsic to the nanostructures. Low-Dimensional TE materials have shown significant improvements in performance over their bulk counterparts. In this spirit, the immediate challenge in area of nanocomposite TE materials is preserving the nanostructures within the bulk composite and the prevention of aggregation and inter-particle growth. In our opinion, the solution significantly depends on the interfaces: a desired interface would prohibit undesired grain boundary growth and inter-diffusion, as well as selectively scatter the phonons and charge carriers. Given this desired result, as well as going beyond the conventional concept of a nanocomposite, we herein propose and demonstrate a novel route to fabricate 2-D nanostructures on the surfaces of the bulk matrix TE materials. To the best of our knowledge, this is the first effort in the field of TE materials research to fabricate coated 2-D nanostructures into the bulk matrix. The thickness, chemical composition and structure, as well as the interplay with the bulk matrix properties should provide the extra degrees of freedom with which to optimize the TE performance of the whole system.

Bo Zhang



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