Thermoelectric Properties of Antimony Based Networks

University dissertation from Stockholm : Department of Materials and Environmental Chemistry, Stockholm University

Abstract: With the retreating sources of carbon based fuels, thermoelectric materials can play an important role in the future of environmentally friendly power generators. Sb based framework have in some cases shown some promising properties as thermoelectric materials. The physical properties may be modified with doping or incorporation of new elements. Zn4Sb3 and Cd4Sb3 are structurally related with a Sb-based network and Zn/Cd occupying the rest of the positions. Both structures undergo order-disorder ?–? transition of the Zn/Cd positions, at 254 K and ~355 K respectively. The previously ordered interstitial atoms become distributed in the structure and the two high temperature phases are isostructural (R-3c). Cd4Sb3 was synthesized from melt-quench, flux synthesis with Sn, Bi and In. The syntheses made with In resulted in interstitial-free ?-Cd4Sb3 with the composition Cd11.7In1.5Sb10. This compound exhibits no phase transitions until decomposition. ZnSnSb2 and InSb both exhibit the cubic sphalerite structure. ZnSnSb2 is metallic and InSb narrow band-gap semiconductor. Attempts were made to fine-tune the electrical properties by probing the mutual solid solubility range. The formula [ZnSnSb2]x[2(InSb)]1-xSn4 and 0<X<1 with 0.1 increments for the whole composition range was used. Resistivity changes from semiconducting to metallic conduction between x=0.9 and x=0.8. In the attempt to dope Zn4Sb3 by In a novel metastable compound with the composition Zn9Sb6In2 was found. Another novel phase was discovered with the composition Zn5Sb4In2-? (?=0.15).  The two phases have the same Sb-framework with a CuAl2 structure. Zn and In arrangements fill the square antiprisms formed by the stacking of 32434 nets in anti configuration. The filling of the antiprisms in the two phases are different, in Zn9Sb6In2 the antiprisms have two filling arrangements, an In or Zn3 triangles. In Zn5Sb4In2-? the antiprisms are filled with an In and a Zn that occupies a split position to form a hetero-atomic dimers.