High valley degeneracy is just one of the peculiar features of PbTe based materials that makes them the most efficient thermoelectric materials for waste heat recovery. Alloying can finely tune the band structure to enhance thermoelectric performance as well as control doping and reduce thermal conductivity.
The rich solid-state chemistry of Zintl phases enables a directed search and optimization of new complex thermoelectric materials. The complex crystal structures of Zintl Phases lead to low phonon velocity and therefore low thermal conductivity while the chemistry of Zintl phases facilitates strategies for tuning the electronic transport.
Skutterudites, based on CoSb3, are the new thermoelectric materials most developed to supplant Bi2Te3 and PbTe based materials in space and commercial applications. Their complex electronic and atomic structures gives them ideal eletrical and thermal properties for thermeoelectrics
Some thermoelectric materials contain fast-diffusing, even 'super-ionic' atoms within a crystalline sublattice of another type of atom. This extraordinary 'liquid-like' behaviour results in an intrinsically low lattice thermal conductivity which enables high zT in an otherwise simple semiconductor.
Interfaces at the nanometer scale can be used to scatter long mean-free-path phonons to reduce the phonon or lattice thermal conductivity and increase zT.