Thermal stability of Mg2Si0.55Sn0.45 for thermoelectric applications
Résumé
Understanding the thermal stability of the Mg2(Si,Sn) system is essential to define their safe tempera-
tures of service. Despite its good thermoelectric performance, Mg2(Si,Sn) is subject to a phase separation
during thermal cycling due to the miscibility gap, which leads to a degradation of its thermoelectric
properties and affects its performance during device operation. Isothermal annealing at 500 !C and
750 !C were performed with different annealing time to investigate thermal stability of Mg2(Si,Sn).
During the heat treatment, two phases were formed associated with porosity in the matrix. In addition,
thickness of specimen was tracked and a significant expansion was detected. This phenomenon is
attributed to the Kirkendall effect. The composition and the structure of the two forming phases were
investigated by electron probe microanalysis and X-ray diffraction. Finally, the optimized thermal
treatment allowed to stabilize the Mg2(Si,Sn) without porosity and the presence of two thermody-
namically stabilized phase (Mg2Si0.41Sn0.59 and Mg2Si0.58Sn0.42) leading to a better reliability of the
silicide thermoelectric modules.
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