学术活动发布与订制系统

A thermoelectric generator directly converts heat into electricity with no moving parts. The long term reliability of these systems has encouraged NASA to use thermoelectric generators in many space probes since the 1960s (up to 30 years unattended). Thermoelectrics could provide a substantial amount of electrical power from residential cogeneration and various sources of waste heat including industrial and geothermal. When connected to an external power supply, a thermoelectric generator becomes a solid-state (Peltier) refrigerator, cooling one end and heating the other. Thus far, the widespread use of thermoelectric generators has been limited by the low material efficiency of the thermoelectric material.

Complex Thermoelectric Materials [1] are ideal because they can exhibit the necessary “electron-crystal, phonon-glass” properties required for high thermoelectric efficiency. Complex crystal structures can lead to high thermoelectric figure of merit (zT) by having extraordinarily low lattice thermal conductivity. A recent example is the discovery that Yb₁₄MnSb₁₁, a complex Zintl compound, has twice the zT as the SiGe based material currently in use at NASA. The high temperature electronic properties of Yb₁₄MnSb₁₁ can be largely understood using models for heavily doped semiconductors and the electron counting rules for Zintl phases. The free hole concentration is set by the stoichiometry and can be modified by the substitution of Al⁺³ for Mn⁺², or La⁺³ for Yb⁺² leading to an increase in the Seebeck coefficient and zT. Substitution of nonmagnetic Zn⁺² for the magnetic Mn⁺² reduces the spin-disorder scattering and further increases zT. Other examples of complex structures studied at Caltech include self assembled thermoelectric composites that resemble epitaxial superlattices in bulk materials.