Liquid phase diffusion bonding and thermoelectric properties of Pb 1-xSnxTe compounds

The solidified Pb_1-xSn_xTe compounds with different x were joined by liquid phase diffusion bonding technique in order to prepare the segmented thermoelectric materials which had a fundamental FGM (functionally graded materials) structure. The Pb_1-xSn_xTe compound is a p-type semiconductor whose carrier concentration increases with increasing x. Therefore the maximum thermoelectric figure of merit of Pb_1-xSn_xTe shifted to a higher temperature with increasing x. A Sn sheet of 50 μm thick was inserted between Pb_1-xSn_xTe compounds as soldering material, and the joining was performed under 2.0 MPa at 700 K for 1800 s in Ar atmosphere. SEM observation revealed that the soldering material reacted with Pb_1-xSn_xTe to form a Sn-rich alloyed layer of less than 2 μm in thickness. No remarkable increase in resistivity was observed in the vicinity of the interface. The joined material showed higher maximum power, P_max, than monolithic materials