Liquid phase diffusion bonding and thermoelectric properties of Pb1-xSnxTe compounds

The solidified Pb1-xSnxTe 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 [1]. The Pb1-xSnxTe compound is a p-type semiconductor whose carrier concentration increases with increasing x [2]. Therefore the maximum thermoelectric figure of merit of Pb1-xSnxTe shifted to a higher temperature with increasing x. A Sn sheet of 50 mu m thick was inserted between Pb1-xSnxTe compounds as soldering material, and the joining was performed under 2.0MPa at 700K for 1800s in Ar atmosphere. SEM observation revealed that the soldering material reacted with Pb1-xSnxTe to form a Sn-rich alloyed layer of less than 2 mu m 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.