20 research outputs found
Optimum electronic structures for high thermoelectric figure of merit within several isotropic elastic scattering models
The influence of impurities on the electric and thermoelectric properties of CdSb single crystals
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In this chapter several aspects of the electronic and phonon structure are
considered for the design and engineering of advanced thermoelectric materials. For
a given compound, its thermoelectric figure of merit, zT, is fully exploited only when
the free carrier density is optimized. Achieving higher zT beyond this requires the
improvement in the material quality factor B. Using experimental data on lead chalcogenides
as well as examples of other good thermoelectric materials, we demonstrate
how the fundamental material parameters: effective mass, band anisotropy, deformation
potential, and band degeneracy, among others, impact the thermoelectric
properties and lead to desirable thermoelectric materials. As the quality factor B is
introduced under the assumption of acoustic phonon (deformation potential) scattering,
a brief discussion about carrier scattering mechanisms is also included. This
simple model with the use of an effective deformation potential coefficient fits the
experimental properties of real materials with complex structures and multi-valley
Fermi surfaces remarkably well—which is fortunate as these are features likely found
in advanced thermoelectric materials
Thermoelectric performance of n -type (PbTe) 0.75 (PbS) 0.15 (PbSe) 0.1 composites
Lead chalcogenides (PbQ, Q = Te, Se, S) have proved to possess high thermoelectric efficiency for both n-type and p-type compounds. Recent success in tuning of electronic band structure, including manipulating the band gap, multiple bands, or introducing resonant states, has led to a significant improvement in the thermoelectric performance of p-type lead chalcogenides compared to the n-type ones. Here, the n-type quaternary composites of (PbTe)0.75(PbS)0.15(PbSe)0.1 are studied to evaluate the effects of nanostructuring on lattice thermal conductivity, carrier mobility, and effective mass variation. The results are compared with the similar ternary systems of (PbTe)1–x(PbSe)x, (PbSe)1–x(PbS)x, and (PbS)1–x(PbTe)x. The reduction in the lattice thermal conductivity owing to phonon scattering at the defects and interfaces was found to be compensated by reduced carrier mobility. This results in a maximum figure of merit, zT, of ∼1.1 at 800 K similar to the performance of the single phase alloys of PbTe, PbSe, and (PbTe)1–x(PbSe)x