In this dissertation, we studied thermal and electronic properties of carbon nanomaterial (CNT and Graphene) incorporated composites by simultaneous control of electronic conduction and thermal transport.
In chapter 2, WS2 is studied as a promising candidate for novel thermoelectric materials due to the high Seebeck coefficient and low thermal conductivity. However, it has a very small electrical conductivity. Thus, we incorporated multiwalled carbon nanotubes (MWNTs) in a WS2 matrix by powder metallurgy to increase electrical conductivity. The insertion of a small amount of MWNTs (0.75 wt%) significantly increased electrical conductivity with a moderate decrease in the Seebeck coefficient and thermal conductivity, leading to an increase in both power factor and thermoelectric figure of merit (ZT), demonstrating that 1-dimensional CNTs with high geometric aspect ratios can be used to improve thermoelectric properties.
In chapter 3, the p-type Bi0.5Sb1.5Te3-graphene composites were prepared by the ball-milled mixing and SPS. Bi2Te3 and Sb2Te3 nanoplates were synthesized by a microwave-assisted solvothermal method. The inclusion of an optimized amount of EG modulated carrier concentration and increased electrical conductivity of composites. Furthermore, it decreased lattice thermal conductivity by phase boundary phonon scatterings. The increased carrier concentration also suppressed the bipolar conduction, which induced slower decrease in Seebeck coefficient and slower increase in bipolar thermal conductivity at higher temperatures. Finally, the ZT increased by 45% by the addition of EG compared with that of the pure Bi0.5Sb1.5Te3 specimen, demonstrating that 2-dimensional graphene can be used as an effective filler to enhance the thermoelectric performance of composites.
In chapter 4, summary of this study and future works will be given.