Decomposition Phenomena of Zn_13−δSb₁₀ under Working Conditions of Thermoelectric Generators and Minimum Current Densities for Electromigration

The mixed ionic-electronic conductor (MIEC) Zn13−δSb10 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−δSb10 (δ ∼ 0.2) prepared by a slow cooling method show zT values of 0.7 at 200 °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 ∼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.