ABSTRACT
The term “clathrate” originates from the Latin word clathratus, which means “protected by cross bars of a grating.” Archetypal compounds are the so-called clathrate hydrates enclosing gaseous or liquid guest species. Intermetallic clathrates are inorganic inclusion compounds structurally related to the hydrates. Over 300 clathrates have been synthesized so far. Among them, clathrates composed of the group 14 elements are regarded as prospective thermoelectric materials that realize the phonon-glass electroncrystal (PGEC) concept proposed by G. A. Slack in 1995 [1]. The PGEC materials are expected to have low thermal conductivity κ like a glass and simultaneously low electrical resistivity ρ like a metal. Such a material may achieve a high value of the dimensionless thermoelectric gure of merit, dened as ZT = α2T/ρκ, if the Seebeck coefcient α is large enough.
