12 research outputs found
Recent advances on thermoelectric materials
By converting waste heat into electricity through the thermoelectric power of
solids without producing greenhouse gas emissions, thermoelectric generators
could be an important part of the solution to today's energy challenge. There
has been a resurgence in the search for new materials for advanced
thermoelectric energy conversion applications. In this paper, we will review
recent efforts on improving thermoelectric efficiency. Particularly, several
novel proof-of-principle approaches such as phonon disorder in
phonon-glasselectron crystals, low dimensionality in nanostructured materials
and charge-spin-orbital degeneracy in strongly correlated systems on
thermoelectric performance will be discussed.Comment: 12 pages, 12 figure
Phonon group velocity and thermal conduction in superlattices
With the use of a face-centered cubic model of lattice dynamics we calculate the group velocity of acoustic phonons in the growth direction of periodic superlattices. Comparing with the case of bulk solids, this component of the phonon group velocity is reduced due to the flattening of the dispersion curves associated with Brillouin-zone folding. The results are used to estimate semiquantitatively the effects on the lattice thermal conductivity in Si/Ge and GaAs/AlAs superlattices. For a Si/Ge superlattice an order of magnitude reduction is predicted in the ratio of superlattice thermal conductivity to phonon relaxation time [consistent with the results of P. Hyldgaard and G. D. Mahan, Phys. Rev. B 56, 10 754 (1997)]. For a GaAs/AlAs superlattice the corresponding reduction is rather small, i.e., a factor of 2â3. These effects are larger for the superlattices with larger unit period, contrary to the recent measurements of thermal conductivity in superlattices