Mechanical Properties of the Interface between Nickel Contact and Extruded (Bi1-xSbx)2(Te1-ySey)3 Thermoelectric Materials

We present detailed studies of the mechanical behavior of electrical contacts since they have a strong effect on the performance and long term reliability of thermoelectric (TE) modules both for cooling and electricity generation. We have studied the mechanical properties of electroplated and electroless plated Ni contacts on n-type and p-type (Bi_1-xSb_x)₂(Te_1-ySe_y )₃ polycrystalline quaternary alloys. These alloys were obtained by mechanical alloying followed by hot extrusion. A variety of surface preparation methods and metallization processes were applied and compared. As soldering alloys we used Sn(60%)Pb(40%) or Sn(95%)Sb(5%) on top of the Ni contacts. Our results show that it is possible to reach mechanical strength above 350 kg/cm² when proper metallization and soldering technologies are applied. Contact reliability becomes especially important for short-legged modules, which provide higher density of cooling and generating power. Extruded TE materials may be the only ones suitable for devices where the required mechanical stress is very high