Role of Deep Defects on the Transport Properties of Polycrystalline Thermoelectric Alloys and Composites

Deep traps at grain boundaries, or within grains, of polycrystalline alloys optimized for large-scale thermoelectric applications affect their transport properties. For an accurate description of these properties, defects require appropriate statistical treatment at the basic level, so that the chemical potential can be obtained as a function of temperature. This work reports on polycrystalline p- and n-type bulk hot-extruded ternary alloys and composites containing Bi, Sb, Te and Se which have advantageous mechanical properties and thermoelectric performance below 500 K. Calculations of the electrical transport properties of heavily doped ternary alloys taking into account their polycrystalline nature provide excellent accord to Hall effect transport measurements in the plane perpendicular to the extrusion axis in the range from 10 K to 440 K. To do so, a statistical treatment of deep donor traps at grain boundaries in p-type composites is required. Ignoring their role may lead to incorrect interpretation of transport measurements.