Thermoelectric Properties of Low-Dimensional Structures at Low Temperatures.

thermoelectric;superlattice;carbon nanotube;Engineering (General);Engineering;Mechanical Engineering

Zhang, KejiaLiang, Xiaogan ;

University of Michigan

关键词: thermoelectric;    superlattice;    carbon nanotube;    Engineering (General);    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/120835/kejiaz_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Thermoelectric energy conversion has a wide range of potential applications but is currently inhibited by low efficiency (as governed in thermoelectric materials by the figure-of-merit ZT). Low-dimensional structures such as superlattices (SLs) and nanowires may offer a new approach to achieve high ZT, particularly at low temperatures where current thermoelectric materials are not as efficient. In this work, the thermal and thermoelectric properties of HgCdTe (MCT) SLs and doped/coated single-walled carbon nanotube (SWCNT) systems have been designed and measured near and below room temperature.A modified 3w method was used to measure both the thermal coductivity and Seebeck coefficient in the cross-plane direction for the SLs. The cross-plane electrical conductivity was determined through a modified transmission line method. The thermal conductivity of long-period SLs was found to be lower than the alloy value, especially at cyrogenic temperatures, and approximately constant over a wide range of temperatures. A comparative method was used to measure the thermal conductivity, electrical conductivity, and Seebeck coefficient of ultralow density SWCNT networks that were either pristine or coated by graphite, BN, or PEDOT:PSS. The thermal and electrical impedances were found to be dominated by intertube junctions in pristine networks and by tubes in coated networks. The thermal and electrical conductivities were found to be lower in coated networks even though they have higher densities,due to strong scattering introduced by coatings. The effects of doping on SWCNT thermal conductivity were studied using molecular dynamics simulations. Phonon dispersion curves and phonon lifetimes were further calculated to examine scattering mechanisms. Substitutional and pyridine-like nitrogen doping was found to reduce thermal conductivity effectively even at low dopant concentrations. Since substitutional nitrogen doping has been shown to increase electrical conductivity in SWCNTs, it provides an interesting alternative to coating in improving ZT in such systems.