Long-time stability of Mg2(Si-Sn-Ge) - based thermoelectrics under large temperature gradient conditions

We study the thermoelectric properties and stability of Mg2(Si-Sn-Ge) composite, prepared by a combination of ball milling process and heating treatment followed by Spark Plasma Sintering and densification. The goal of this study is to investigate the long-time stability of the efficient n-type thermoelectric material under conditions similar to those in future applications. Rectangular samples with dimensions 6x6x15 mm3 were placed in an Ar-filled chamber, equipped with thermoelectric cooling module and with a heater. The thermoelectric power and electrical resistivity of the sample were measured while temperatures of 800K at the hot side, and 320K at the cold side of the sample were maintained for more than 300hours. Different aspects of the sample stability were investigated: 1. mechanical stability under global and local thermal cycling; 2. chemical stability of the sample-electrode contacts; 3. sample stability at high temperatures; 4. material stability under large thermal gradients.