Role of Structures on Thermal Conductivity in Thermoelectric Materials

Abstract

The figure of merit ZT = σα 2 T/λ (α the Seebeck coefficient, σ and λ the electrical and thermal conductivity, respectively) is an essential element of the efficiency of a thermoelectric material for applications, which convert heat to elec- tricity or, conversely, electric current to cooling. From the expression of the power factor, σα 2 , it was deduced that a highly degenerated semiconductor is necessary. In order to reduce the lattice part of the thermal conductivity, various mechanisms, mainly related to the structure of the materials, were tested in new thermoelectric materials and had been the topics of different reviews. These include cage-like ma- terials, effects of vacancies, solid solutions, complex structures (cluster, tunnel, ... ), nano-structured systems. We plan to review structural aspects in the modern ther- moelectric materials and to include results of the very recent years. Moreover, as micro- and nano-composites seem to be promising to increase ZT in large size sam- ples, we will also briefly discuss the interest of spark plasma sintering technique to preserve the micro- or nano-structure in highly densified samples.