ICT2014 Abstracts

Increasing the thermoelectric figure of merit can be approached via two general methods, nanostructuring to reduce the lattice thermal conductivity and altering the band structure to improve the power factor. Multiple methods of band structure engineering in the valence band of p-type PbTe thermoelectric materials have shown improvements in ZT like in the PbTe-PbSe, PbTe-TlTe, and PbTe-SrTe systems. However, band structure engineering the conduction band in n-type PbTe thermoelectrics is relatively unexplored. Herein, we investigate band structure alignment between the secondary phases CdS and CdSe with the PbTe matrix in an n-type system. Despite the large difference in the band gaps between the secondary phase and matrix, carrier mobility will result in minimal losses if the energy difference between the conduction band edges is minimal. This strategy has been demonstrated in p-type PbTe-SrTe, PbSe-(CdS/ZnS), and PbS-CdS systems. By aligning the valence band of the matrix and precipitate, high power factors can be maintained while reducing the lattice thermal conductivity by increasing phonon scattering with nanoprecipitates of the secondary phase. The nature of the band alignment between CdSe and CdS with PbTe will be compared with DFT calculations and experimental results. Changes in mobility, power factor and reductions in lattice thermal conductivity will also be discussed and compared to the literature