| Thermoelectric cooling devices are limited by poor efficiencies. If better thermoelectric materials could be found, the potential applications for thermoelectric cooling are numerous. The central challenge is to find materials with large figures of merit Z, or more specifically, dimensionless figures of merit ZT ≥ 1. Here T is the temperature and Z is a combination of the materials' transport properties: Z = S2/rhokappa where S is the thermopower or Seebeck coefficient, rho is the electrical resistivity, and kappa is the thermal conductivity. The current state-of-the-art materials are small band gap semiconductors with ZT ≈ 1. One potential source of new materials is a class of rare earth intermetallics known as intermediate valence compounds. In these systems, the interaction of the 4f electrons with the conduction electrons leads to a variety of unique properties, including high thermopowers.;This dissertation concentrates on developing the procedures to evaluate thermoelectric materials, as well as exploring the chemistry and physics of several potentially interesting chemical systems. The materials focus is on cerium intermediate valence intermetallics, although some work on tellurium based compounds is presented. Of the few known intermediate valence materials, the highest ZT is observed in CePd3 (∼0.2 at room temperature). Part of this dissertation involves trying to modify CePd3 to achieve higher ZT values. Other cerium based compounds are also investigated: RE 3M3Sb4 (RE = Ce, Nd; M = Cu, Pt), CeMAs2 (M = Cu, Ag, Au) and CeM2-xNx (M = late transition metal; N = Si, Ge). The Kondo insulator Ce3Pt3Sb 4 is particularly interesting because of its combination of intermediate valence and semiconducting electrical resistivity. The properties of Ce 3Pt3Sb4 are explored as a function of chemical doping and pressure. While no breakthrough thermoelectric materials have been discovered, this work has led to a greater understanding of the challenges involved in exploring these types of compounds. |
