Synthesis of skutterudites as thermoelectric materials

Research in the field of thermoelectric materials is focused on finding a material with a high figure of merit, the numerical expression for the usefulness of a potential thermoelectric material. The best material must be a good electrical conductor and a poor thermal conductor at the same time. One group of materials that can meet this requirement is the family of skutterudite compounds. Skutterudite compounds are cage-like materials which accommodate an atom in the interstitial void also referred to as the "cage". This results in the reduction of the lattice thermal conductivity.; The interstitial atom is loosely bound to its surrounding cage structure resulting in thermodynamic instability. This makes it extremely difficult to synthesize the filled skutterudite compounds, since traditional solid state synthesis utilizes high temperatures to overcome slow solid state diffusion rates. Many attempts to synthesize ternary skutterudites have resulted in the formation of the skutterudite phase along with significant impurities. Others have stated that in order to achieve complete filling of the structure charge compensation is necessary.; In this dissertation, the synthesis of a series of new, metastable ternary crystalline compounds with the skutterudite crystal structure is presented. The limitations of traditional solid state synthesis can be overcome by using multilayer precursors. Modulated elemental reactants form amorphous reaction intermediates and crystallize at temperatures around 200°C in a controlled fashion to form phase pure skutterudites. Composition as well as structure of the product can be controlled.; Several series of skutterudite compounds were synthesized and analyzed. Preliminary measurements of thermoelectric properties on thin films suggested that bulk measurements were necessary. A new method that extends the use of elementally modulated layers to the synthesis of bulk samples was developed. Samples were produced in quantities of approximately 500mg. This allows for the measurement of bulk thermoelectric properties that will be relevant should the compound be used in a thermoelectric device. Results for the thermal conductivity collected on a series of ternary skutterudite samples showed that the properties of these newly accessible compounds are indeed very promising.; This dissertation includes my previously published materials.