Growth and characterization of novel thermoelectric materials

This thesis describes a concerted effort to study the transport properties of a family of novel thermoelectric materials called skutterudites. Specifically, my investigations concern antimonide skutterudites in both their simple, unfilled forms typified by CoSb{dollar}sb3{dollar} as well as the filled variants of the material represented by the {dollar}rm CeFesb{lcub}4-x{rcub}Cosb{lcub}x{rcub}Sbsb{lcub}12{rcub}{dollar} structure. In addition to the bulk forms of the material, I explored the growth of the skutterudites in their thin film forms.; Low temperature transport studies of CoSb{dollar}sb3{dollar} single crystals show unusually large hole mobilities (up to 3000 {dollar}rm cmsp2Vsp{lcub}-1{rcub}ssp{lcub}-1{rcub}{dollar} at room temperature), and power factors. Our studies helped to elucidate the nature of the transport in this compound and we were able to make a meaningful comparison with the band-structure calculations. Our findings lend support to the picture that these skutterudites possess a highly nonparabolic valence band.; We investigated the effect of Co doping on the transport properties of filled skutterudites, {dollar}rm CeFesb{lcub}4-x{rcub}Cosb{lcub}x{rcub}Sbsb{lcub}12{rcub}{dollar} with {dollar}rm0le xle2.{dollar} We found that the addition of Co causes a decrease in hole concentration and a corresponding increase in thermopower as electrons fill the holes in the valence band. We also found that the amount of Ce that can be placed in the voids of the structure decreases with increasing Co concentration. Our findings suggest that the thermoelectric properties in these filled skutterudites could be optimized via Co doping.; We also investigated the thermoelectric properties of partially filled skutterudites {dollar}rm Cesb{lcub}delta{rcub}Cosb4Sbsb{lcub}12{rcub}{dollar} with {dollar}0ledeltale0.1.{dollar} We found that a small amount of Ce, as little as 0.05, could significantly reduce the thermal conductivity of the filled skutterudites. Furthermore, we found that the presence of Ce leads to an n-type character of transport. In spite of only moderate electron mobilities in these n-type skutterudites, we found that they could have figure of merit (ZT {dollar}sim{dollar} 0.15) that is comparable or even exceeds the values for the p-type skutterudites at room temperature due to their large effective carrier masses.; Finally, we explored the growth conditions of RhSb{dollar}sb3{dollar} thin films on a variety of substrates, such as Si (111), {dollar}rm Alsb2Osb3{dollar} (110) and synthetic mica (001) and found that the RhSb{dollar}sb3{dollar} thin films are best grown at low temperature (around 300{dollar}spcirc{dollar}C) followed by annealing at high temperature (around 500{dollar}spcirc{dollar}C). RhSb{dollar}sb3{dollar} (111) thin films on synthetic mica of high structural quality have been obtained. Thermoelectric properties of some of the films were studied.