S. Sportouch

Observed properties and electronic structure of RNiSb compounds (R = Ho, Er, Tm, Yb and Y). Potential thermoelectric materials

The RNiSb compounds (R=Ho, Er, Tm, Yb and Y) and some selected solid solution members such as (Zr 1-x Er x )Ni(Sn 1-x Sb x ) and ErNiSb 1-x Pn x (Pn=As, Sb, Bi) have been studied. They all crystallize in the MgAgAs structure type, which can be considered as a NaCI structure type in which half of the interstitial tetrahedral sites are occupied by Ni atoms. The measured values of the Seebeck coefficients, at room temperature, are positive for RNiSb (R=Ho, Er, Yb and Y) compounds and ErNiSb 1-x Pn x (Pn=As, Sb, Bi) solid solutions, but for (Zr 1-x Er x )Ni(Sn 1-x Sb x ) members vary from negative to positive values when 0

Measurement system for doping and alloying trends in new thermoelectric materials

Several new materials in the A/sub 2/Bi/sub 8/Se/sub 13/, (A=K, Rb, Cs), HoNiSb, Ba/Ge/B (B=In, Sn), and AgPbBiQ/sub 3/ (Q=S, Se, Te) systems have shown promising characteristics for thermoelectric applications. To accommodate the large number of samples required for doping and alloying studies, a new measurement system has been designed with a high sample throughput. A second system is then utilized for complete characterization of the most promising samples. This paper presents a description of the systems and measurement techniques involved, with preliminary data on some of the above mentioned compounds.

Thermoelectric properties of the cubic family of compounds AgPbBiQ3 (Q = S, Se, Te). Very low thermal conductivity materials

The AgPbBiQ 3 class of compounds and their solid solution members are related to the NaCl structure type, where Ag, Pb and Bi atoms are statistically disordered on the Na site and Q atoms occupy the Cl site. These compounds were synthesized by combining the elements in the appropriate ratio and heating under static vacuum at 900° C for 3 days. They are narrow gap semiconductors with band gaps in the range of 0.6 to 0.28 eV. The charge-transport properties were measured on ingots as a function of temperature. The compounds AgPbBiTe 3 , AgPbBiSe 3 , AgPbBiTe 2.75 Se 0.25 and AgPbBiTe 2 Se, undoped, possess an electrical conductivity in the range of 70 S/cm to 400 S/cm. These materials exhibit negative thermopower ranging from -40 μV/K to -160 μV/K at room temperature and thermal conductivity less than 1.30 W/mK.

Thermoelectric properties of half-Heusler phases: ErNi/sub 1-x/Cu/sub x/Sb, YNi/sub 1-x/Cu/sub x/Sb and Zr/sub x/Hf/sub y/Ti/sub z/NiSn

Our previous investigations on the half-Heusler phases, rare earth nickel antimonides and zirconium nickel stannides, have indicated that ErNiSb can be comparably promising to ZrNiSn for further thermoelectric investigations. These compounds crystallize in the cubic MgAgAs structure type and possess Seebeck coefficients up to +160 /spl mu/V/K and -355 /spl mu/V/K, respectively. Their thermal conductivities are approximately 60 mW/cm.K with their electrical conductivity curves resembling a semiconductor (350 S/cm and 250 S/cm for ErNiSb and ZrNiSn, respectively). The rare earth nickel antimonide compounds are synthesized as p-type materials, however, a careful analysis of their electronic band structures point out that n-type materials will possess larger effective masses and therefore larger Seebeck coefficients. Consequently, in order to improve the transport properties of these compounds and to achieve n-type materials, we investigated some of their solid solutions obtained by partial substitution of the transition metal element. Here, we report the transport properties of a wide range of solid solution members corresponding to the formula ErNi/sub 1-x/Cu/sub x/Sb, YNi/sub 1-x/Cu/sub x/Sb and Zr/sub x/Hf/sub y/Ti/sub z/NiSn (x+y+z=1).