I. A. Nishida

Thermoelectric properties of boron doped iron disilicide

B doped /spl beta/-FeSi/sub 2/ has high thermal shock resistance. The effect of B doping on thermoelectric properties of /spl beta/-FeSi/sub 2/ has been investigated. B doped FeSi/sub 2/ was a solid solution in the composition range 0<x/spl les/0.03. It was found that B atoms acted as donors in the whole composition range of x. The Seebeck coefficient of FeSi/sub 2/ was almost six times higher and also electrical resistivity was less than a quarter by B doping, because of hopping conduction. Lattice thermal conductivity was reduced by 20% by B doping of x=0.03. Mn doped p-type FeSi/sub 2/ has even lower effective maximum power P/sub eff/ by B doping, while P/sub eff/ of Co doped n-type samples was not affected by the doping. High thermal shock resistance was successfully given to Co doped n-type FeSi/sub 2/ by B doping.

Temperature dependence of the figure-of-merit of Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/

The p-type Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule was unidirectionally grown using a Bridgman furnace and subsequently rapidly cooled by Ar to form a Widmannstatten structure of a high temperature phase AgSbTe/sub 2/, which could be desirable for power generation. Though the boule looked a homogeneous Widmannstatten structure, XRD patterns revealed that some precipitates of Ag/sub 2/Te and Sb/sub 2/Te/sub 3/ were contained in the boule and increased in volume in the growth direction. The figure-of-merit Z of the p-type Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule have been evaluated in the temperature range from 300 to 700 K. The maximum figure-of-merit Z/sub max/ was different in the portions of the boule. The value of 2.0/spl times/10/sup -1//K was at 620 K for the former half portion of the boule and that of 1.7/spl times/10/sup -3//K was at 585 K for the latter half portion. The Ag/sub 0.208/Sb/sub 0.275/Te/sub 0.517/ boule with less precipitates showed higher Z at higher temperatures.

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.

Thermoelectric properties of segmented Bi/sub 2/Te/sub 3//PbTe

The sintered Bi/sub 2/Te/sub 3/ and PbTe compounds were joined by soldering with flux to form segmented materials. The joining with flux was performed under 2 MPa at 650 K for 10s in a N/sub 2/ atmosphere. Soldering with ultrasonic wave was also attempted. Te-Ag eutectic alloy was used as the solder. SEM observation revealed that the solder did not form any undesirable layer in the vicinity of the joined part in both segmented materials formed by both soldering ways. No remarkable increase in resistivity was observed at the interface. The segmented materials showed higher power factor than each monolithic material at the temperature range between 400 K and 650 K.