Why are clathrates good candidates for thermoelectric materials?

Clathrates are periodic solids in which tetrahedrally coordinated atoms-for m cages that surround a metal atom. We examine Slack's suggestion that the metal atoms scatter phonons but not electrons, thus lowering the thermal bu t not the electric conductivity. If this is true, as transport measurements indicate, these compounds are promising thermoelectric materials, (C) 2000 Academic Press.