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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Thermal Conductivity of Individual Boron Carbide Nanowires




Abstract

Boron carbides represent a class of ceramic materials that possess complex molecular structure and composition. Despite of being projected as a promising candidate for high temperature thermoelectric energy conversion, their transport properties are still not well characterized. One major obstacle is that bulk boron carbides are usually polycrystalline with varying grain size and carbon concentration. This, combined with their complex molecular structure, poses a significant challenge to establish a comprehensive structure-property relation. We have synthesized single crystalline boron carbide nanowires, which make good specimens for transport property study. The nanowires could possess axial or transverse stacking faults with varying stacking fault densities to explore the effects of stacking faults on energy transport, which is still not fully understood. Our results indicate that as long as the stacking fault is of the same orientation, the stacking fault density has marginal effects on thermal conductivity over a temperature range of ~30-400 K. Intriguingly, for nanowires with a kink and/or stacking faults orientation alteration, significantly lower thermal conductivities were observed as compared to corresponding straight ones. One more important observation is that all the measured thermal conductivity is lower than 7 W/m-K, lower than the single crystalline bulk data (30 W/m-K), indicating that the boundary scattering still plays an important role in thermal transport in complex boron carbide structures. Preliminary tests showed the room temperature thermoelectric figure of merit is enhanced to be twice the reported bulk value, indicating a strong potential of engineering boron carbides for thermoelectric applications.

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