ABSTRACT
Many scienti›c approaches, both experimental and theoretical/computational, have been brought to bear on the problem of thermoelectric materials science. še ultimate goal of these studies is, of course, to maximize the thermoelectric ›gure of merit Z of a material. Large Z paves the way for many applications in both power generation and solid state heating and cooling. še ›gure of merit itself is comprised of the three fundamental transport parameters of Seebeck coe´cient (S), electrical conductivity (σ), and thermal conductivity (κ) and is given by the equation
Z S=
2σ κ
(12.1)
Even a precursory examination of Equation 12.1 reveals the conundrum of thermoelectricity: this particular combination of these three parameters is not conducive to producing high ›gure of merit. še tendency in nature is that, for instance, high electrical conductivity σ, as in a good metal like copper or silver, is accompanied by minute Seebeck coe´cient, and vice versa; and similarly high electrical conductivity also implies high thermal conductivity. šese “contraindicated” properties have frustrated the development of materials with high ›gure of merit for decades if not centuries. Noting that the dimensions of Z are inverse temperature, it is traditional to classify thermoelectric materials by the
12.1 Introduction .................................................................................... 12-1 12.2 Electronic Band Structure of Transition-Metal
Aluminides and Silicides ............................................................... 12-2 12.3 Implications for šermoelectricity .............................................. 12-3 12.4 Full Heusler Alloys Based on Fe2VAl ...........................................12-4 12.5 Alloys Based on CoSi .....................................................................12-6 12.6 Summary ..........................................................................................12-9 References ....................................................................................................12-9
dimensionless quantity ZT, where T is the absolute temperature. Despite intense experimental and theoretical scrutiny of this problem, few thermoelectric materials have been discovered with ZT values exceeding unity. New approaches continue to be brought to bear on this issue in the hopes that materials with much higher ›gure of merit can be realized.
