Thermoelectric Power Generation by Clathrates

Abstract

Clathrate compounds combine aesthetic beauty of their crystal structures with promising thermoelectric properties that have made them one of the most explored family of compounds deemed as base for thermoelectric generators for mid-and hightemperature application. This chapter surveys crystal and electronic structure and structure-related transport properties of selected types of clathrates and discusses their thermoelectric performance and prospects of their future applications.

Crystal Chemistry and Thermoelectric Properties of Type-I Clathrate Ba8Ni∼3.8SixGe42.2−x (x = 0, 10, 20, 42.2)

“…As representatives of phonon glass–electron crystal (PGEC) materials, intermetallic type-I clathrates have been attracting great attention for fundamental investigations and potential applications in the field of thermoelectricity [1,2,3,4,5,6,7,8,9,10]. The crystal structure of type-I clathrate contains covalently bonded frameworks with elements mainly from groups 13 and 14 in the periodic table, forming cages for metal atoms to fill [8,9,11].…”

“…The crystal structure of type-I clathrate contains covalently bonded frameworks with elements mainly from groups 13 and 14 in the periodic table, forming cages for metal atoms to fill [8,9,11]. The rattling of the metal atoms in these cages was generally considered as the root for the low lattice thermal conductivity in type-I clathrates [5,6,8], which benefits the high thermoelectric (TE) performance determined [1,12,13,14,15] by $ZT=S^2\sigma T/({\kappa }_e+{\kappa }_{ph})$.…”

“…However, it is challenging due to the inversion relations between these parameters [16]. Substitution/doping with transition metal (TM) elements for the framework atoms is usually effective to optimize the charge carrier concentration [8,9,11,17,18,19,20,21,22,23,24,25,26,27,28], which is frequently guided by the Zintl law because type-I clathrates are considered as Zintl compounds [8,9,11,29,30]. The substituted TM elements generally have different valences from the framework atoms.…”

“…The transport properties can then be tailored by changing the TM content. However, vacancies, which are typical in type-I clathrates (especially in Ge containing clathrates) [8,9,11], should be considered in the use of the Zintl law. They accept electrons and reduce the residual carrier concentrations.…”

“…They accept electrons and reduce the residual carrier concentrations. The content of vacancies in the crystal structure is generally difficult to control, as it depends on many factors such as the type of metals in the cages, the substitution level of a TM element for the framework, and the material synthesis process [8,9]. It is even still challenging to precisely define the quantity.…”