Thermoelectric properties of Ba8GaxGe46-x clathrate compounds

Polycrystalline Ba₈Ga_xGe_46-x clathrate compounds with different Ga compositions (nominal x=12-20) have been grown by arc melting and spark plasma sintering techniques and the effects of Ga composition on the thermoelectric properties have been investigated. The conduction carrier type of the compounds altered from n-type (x=12-16) to p-type (x=17-20). Varying the Ga composition could successfully control the carrier concentration. The (absolute) Seebeck coefficient values for p-type compounds were found to be larger than those for n-type compounds. The lattice thermal conductivity values for both n- and p-type compounds were extremely low (∼0.01 W/cmK). The estimated thermoelectric figure of merit ZT values reach ∼1 for both n-type (x=15) and p-type (x=18) compounds. Therefore, it was found that the thermoelectric properties of Ba₈Ga_xGe_46-x clathrate compounds could be significantly improved by optimizing the Ga composition.