By Megan Tan ‘19
Thermal and electrical conductivity need to be proportional in electrical conductive solids. Although several metals can conduct electricity better than they can conduct heat, this phenomenon has only been known to occur at extreme temperatures. However, a recent study led by Professor Junqiao Wu from the University of California, Berkeley and his team of researchers has found that metallic vanadium dioxide can conduct electricity without conducting heat.
Vanadium dioxide exhibits certain unconventional properties, such as its ability to switch from an insulator to a metal at 152 degrees Fahrenheit and its transparent appearance below 86 degrees Fahrenheit. Using results from simulations and X-ray scattering experiments, Wu calculated the phonon dispersions using the density functional theory for vanadium dioxide in bulk and in a nanobeam. The phonon thermal conductivity was then calculated by subtracting the nanobeam phonon thermal conductivity value from the measured value. The results showed that the thermal conductivity attributed to the electrons is ten times smaller than expected in other metals. This was caused by the electrons moving in unison with each other and not in the random motion that was expected. In this fluid-like motion, there are fewer configurations available for electrons to randomly hop between, causing heat transfer to be less efficient. More significantly, the study also showed that the electric and heat conductivity in vanadium dioxide can be altered by mixing it with other materials. When vanadium dioxide was mixed with tungsten, the samples turned metallic at a lower temperature, and it also caused the electrons to conduct heat more efficiently.
This thermal conductivity research is significant because it could lead to a wide range of applications in thermos-conductivity, such as stabilizing temperature and dissipating heat, potentially leading to more efficient engines. Researchers can also test vanadium dioxide with other elements in the periodic table to examine the electrical and heat conductivity for future research.
- J. Wu et al., Anomalously low electronic thermal conductivity in metallic vanadium dioxide, Science 355, 371-374 (2017). doi: 10.1126/science.aag0410.
- Image retrieved from: http://www.mse.berkeley.edu/~jwu/publications/Lee-Science2017.pdf