Lead-free thermoelectrics: High figure of merit in p-type AgSn _mSbTe _m+2

Thermoelectric materials based on Pb-free compositions are of considerable current interest in environmentally friendly power-generation applications derived from waste-heat sources. Here, a new study of the thermoelectric properties of the tin-based compositions with the general formula AgSn _mSbTe _m+2 (m = 2, 4, 5, 7, 10, 14, 18) is presented, where the m value is used as the tuning parameter of the thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity are measured from 300 K to 723 K and the resulting thermoelectric figure of merit is determined as a function of the SnTe/AgSbTe ₂ ratio. A thermoelectric figure of merit ZT ≈1 is obtained at 710 K for m = 4, indicating that the system AgSn _mSbTe _m+2 holds great promise as an alternative p-type, lead-free, thermoelectric material.