N-type Lead-Chalcogenide Thermoelectric Materials Alloyed with Tin

N-type conduction was observed in epitaxial Pb 1-x Sn x Se and Pb 1-x Sn x Te thin films grown by MBE with an increasing charge carrier concentration as well as an increasing thermopower value related to an increasing tin content reaching up to 12at%. The lattice thermal conductivity decreases as expected due to alloy scattering but the carrier mobility is almost stable. All these effects increase strongly the thermoelectric properties of Pb 1-x Sn x Se and Pb1-xSnxTe. The n-type conduction arises from a metal excess in the stoichiometry range. The same type of conduction has also been found in bulk samples. Bulk single crystals of Pb 1-x Sn x Se and Pb 1-x Sn x Te are grown by the unseeded vapor growth technique. A rather constant mobility and a decreasing thermal conductivity with increasing tin content are measured in the n-type bulk samples. A figure of merit of ZT=0.9 was measured at 325°C for a Pb 0,965 Sn 0,035 Se sample with a carrier concentration of about 9.3E18 cm -3 , i.e. already better than known n-type PbTe-based materials for this temperature range.