Liquid phase diffusion bonding and thermoelectric properties of Pb/sub 1-x/Sn/sub x/Te compounds

The solidified Pb/sub 1-x/Sn/sub x/Te 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/sub 1-x/Sn/sub x/Te compound is a p-type semiconductor whose carrier concentration increases with increasing x. Therefore the maximum thermoelectric figure of merit of Pb/sub 1-x/Sn/sub x/Te shifted to a higher temperature with increasing x. A Sn sheet of 50 /spl mu/m thick was inserted between Pb/sub 1-x/Sn/sub x/Te 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/sub 1-x/Sn/sub x/Te to form a Sn-rich alloyed layer of less than 2 /spl 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/sub max/, than monolithic materials.