Heat transport in nanoscale carbon materials such as carbon nanotubes and graphene is normally dominated by phonons. Here, measurements of in‐plane thermal conductivity, electrical conductivity, and thermopower are presented from 77–350 K on two films with thickness <100 nm formed from semiconducting single‐walled carbon nanotubes. These measurements are made with silicon–nitride membrane thermal isolation platforms. The two films, formed from disordered networks of tubes with differing tube and bundle size, have very different thermal conductivity. One film matches a simple model of heat conduction assuming constant phonon velocity and mean free path, and 3D Debye heat capacity with a Debye temperature of 770 K. The second film shows a more complicated temperature dependence, with a dramatic drop in a relatively narrow window near 200 K where phonon contributions to thermal conductivity essentially vanish. This causes a corresponding large increase in thermoelectric figure‐of‐merit at the same temperature. A better understanding of this behavior can allow significant improvement in thermoelectric efficiency of these low‐cost earth‐abundant, organic electronic materials. Heat and charge conductivity near room temperature is also presented as a function of doping, which provides further information on the interaction of dopant molecules and phonon transport in disordered nanotube films.
In this study, we report a large magneto-thermal conductivity effect, potentially usable in heat flow switches and thermoelectric devices, in Ag2Te over a wide temperature range, including room temperature. When a magnetic field of μ0H = 9 T is applied to Ag2Te at 300 K along the direction perpendicular to the heat and electric currents, the thermal conductivity κ decreases by a remarkable 61%. This effect is mainly caused by the suppressed electronic thermal conductivity in association with a significant magnetoresistance effect, but the suppression of the thermal conductivity is larger than that of the electrical conductivity, presumably due to a field-induced decrease in the Lorenz ratio. Its very low lattice thermal conductivity, as low as 0.5 W m−1 K−1, also greatly contributes to the large relative magneto-thermal conductivity effect. The significant decrease in thermal conductivity and the 18% increase in the Seebeck coefficient S lead to a nearly 100% increase in the thermoelectric figure of merit zT = S2σTκ−1 despite the 43% decrease in electrical conductivity σ.
more » « less- Award ID(s):
- 2011876
- PAR ID:
- 10512997
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- AIP Advances
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2158-3226
- Page Range / eLocation ID:
- 015016
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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