Decomposition Phenomena of Zn13-δSb10 under Working Conditions of Thermoelectric Generators and Minimum Current Densities for Electromigration

The mixed ionic-electronic conductor (MIEC) Zn13-delta Sb10 is a thermoelectric material with high performance at intermediate temperatures and contains only abundant elements. This work evaluates its suitability for thermoelectric applications with respect to thermal instability and decomposition by electromigration of Zn under current flow. In addition to the formation of Zn whiskers, this migration often leads to cracks. Thermoelectric measurements of bulk Zn13-delta Sb10 (delta similar to 0.2) prepared by a slow cooling method show zT values of 0.7 at 200 degrees C. A series of tests under flowing currents with different voltages and current densities on bar-shaped samples was followed by the space-resolved investigation of their composition and its systematical correlation with the Seebeck coefficient. The latter increases upon Zn depletion, especially when ZnSb is formed. At room temperature (RT), Zn migration starts at a voltage of similar to 0.01 V, which is much lower than for other MIECs like copper chalcogenides. At higher electrical fields, which may be enhanced by the Seebeck voltage, the amount of deposited Zn at the negative pole increases with the current density even if the transported charge is kept constant.