Why are clathrates good candidates for thermoelectric materials?

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