SiGe/electrode response to long-term high-temperature exposure

Joints between an n-type Si0.8Ge0.2(P0.3 atomic %) thermoelectric semiconductor and carbon electrodes were prepared by hot-pressing with thin sheets of titanium foil inserted between them at 1528K in a vacuum. The content of phosphorous, measured using an Inductively Coupled Argon Plasma Emission Spectrometer, decreased from 0.20% to 0.11% after joining. To evaluate the upper limit of heating dependence, the SiGe/carbon electrode was exposed in an argon atmosphere at 1273K and 1373K for 300 hours, after which the resistance and Seebeck coefficient were measured. These results showed that the power factor (alpha(2)sigma) could be effectively evaluated using the Larson-Miller Parameter (C=13.3). SEM and EPMA observations showed the presence of many voids in the junction layer of the SiGe/carbon electrode after exposure. The titanium atoms were enriched in the junction layer, and started diffusing at a temperature of 1273K or over.