Ag/sub 9/TlTe/sub 5/ and AgTlTe: high ZT materials with extremely low thermal conductivity

We have studied the thermoelectric properties Ag/sub 9/TlTe/sub 5/ and AgTlTe. The thallium compounds have extremely low thermal conductivities around 0.25 Wm/sup -1/K/sup -1/ from room temperature to about 700 K. The thallium compounds indicate very high ZT values; especially the highest ZT value of Ag/sub 9/TlTe/sub 5/ is 1.23 obtained at 700 K. Ag/sub 9/TlTe/sub 5/ is a unique material combining extremely low thermal conductivity and relatively low electrical resistivity.