Thermoelectric properties of Ba/sub 8/Ga/sub x/Ge/sub 46-x/ clathrate compounds

Polycrystalline Ba/sub 8/Ga/sub x/Ge/sub 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 (/spl sim/0.01 W/cmK). The estimated thermoelectric figure of merit ZT values reach /spl sim/1 for both n-type (x=15) and p-type (x=18) compounds. Therefore, it was found that the thermoelectric properties of Ba/sub 8/Ga/sub x/Ge/sub 46-x/ clathrate compounds could be significantly improved by optimizing the Ga composition.