What A Difference A Neutron Makes

For the first time, scientists have demonstrated that modified hydrogen bonding is sufficient to switch solid-state electronic properties.

AsianScientist (Oct. 9, 2014) – By simply replacing hydrogen with deuterium, scientists have successfully developed a purely organic material that can simultaneously switch both its electrical and magnetic properties. This research has been published in the Journal of the American Chemical Society.

Hydrogen bonds (H-bonds) are essential in many biological and chemical processes; causing water to turn into ice and linking atoms and ions in DNA and proteins and so on. By altering the formation of H-bonds, it is theoretically possible to cause switches in the dielectric, ionic and magnetic properties of materials. However, successful examples of such switching based on hydrogen bonding are limited to a small subset of physical properties such as dielectric properties.

In the present study, led by Professor Hatsumi Mori from the Institute for Solid State Physics at the University of Tokyo, researchers studied whether the physical properties of a material could be controlled by using deuterium instead of hydrogen. Deuterium is an isotope of hydrogen, possessing the same number of protons as hydrogen but containing one additional neutron.

The research team worked with the purely organic crystal κ-H3(Cat-EDT-TTF)2 (abbreviated as κ-H), which has a unique structure of two equivalent (Cat-EDT-TTF) skeletons with a +0.5 charge linked by a symmetric strong H-bond. By replacing three hydrogen atoms with deuterium, the authors formed a new material they called κ-D.

At temperatures below 185K, both κ-H and κ-D had paramagnetic and semiconductor properties. However, at temperatures above 185K, κ-D showed a profound switch in physical properties, transforming into a non-magnetic insulator. Subsequent X-ray crystal structure analysis showed that this dramatic switching was due to the displacement of deuterium within the H-bond, accompanied by electron transfer between the two (Cat-EDT-TTF) to form an asymmetric H-bond.

The present demonstration of H-bond based switching of solid-state electronic properties is unprecedented. The research team anticipates that their discovery will not only spur further developments in basic science, but will also have applications in developing new types of devices with switching functionality and purely organic thin-film semiconducting and magnetic materials.

The article can be found at: Ueda et al. (2014) Hydrogen-Bond-Dynamics-Based Switching of Conductivity and Magnetism: A Phase Transition Caused by Deuterium and Electron Transfer in a Hydrogen-Bonded Purely Organic Conductor Crystal.


Copyright: Asian Scientist Magazine; Photo: University of Tokyo.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Rebecca did her PhD at the National University of Singapore where she studied how macrophages integrate multiple signals from the toll-like receptor system. She was formerly the editor-in-chief of Asian Scientist Magazine.

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