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Daniel I. Bilc, Geoffroy Hautier, David Waroquiers, Gian-Marco Rignanese, and Philippe Ghosez. Low-Dimensional Transport and Large Thermoelectric Power Factors in Bulk Semiconductors by Band Engineering of Highly Directional Electronic States. Physical Review Letters, 114, p. 136601, 2015.

Rezumat: Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by
low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but
less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band
structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures
and the introduction of resonant states were suggested as possible solutions to this paradox, but with limited
success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors.
It exploits the highly directional character of some orbitals to engineer the band structure and produce a
type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic
properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler
compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room
temperature. Our findings are totally generic and rationalize the search of alternative compounds with
similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic,
superconducting, or photovoltaic applications.

Cuvinte cheie: Low-Dimensional Transport, Thermoelectric Materials

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