February 19, 2021
Tokai National Higher Education and Research System, Nagoya University
Chiba University
Keio University
Japan Synchrotron Radiation Research Institute (JASRI)
A research group from the Graduate School of Engineering, Nagoya University, Tokai National Higher Education and Research System, led by Associate Professor Naoyuki Katayama, master's student Keita Kojima (also a visiting graduate student at the Japan Synchrotron Radiation Research Institute), Shinya Tamura (then a master's student), and Professor Hiroshi Sawa (also a visiting researcher at JASRI), has discovered that an inorganic crystal composed of lithium, vanadium, and sulfur exhibits lattice dynamics similar to those of a plastic crystal. The discovery was made in a joint research project with Professor Akira Saito and master's student Sosuke Hattori of the Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University; Professor Yukinori Ohta and doctoral student Tomonori Yamaguchi of the Graduate School of Science, Chiba University; Assistant Professor Koudai Sugimoto of the Faculty of Science and Technology, Keio University; and Postdoctoral Researcher Shintaro Kobayashi and Senior Scientist Koji Ohara of JASRI.
In some solid crystals where atoms are regularly arranged, the lattice spontaneously deforms to form regular patterns when cooled to low temperatures. These characteristic patterns were thought to exist stably only at low temperatures and to disappear above a characteristic temperature called the phase transition temperature. In the inorganic crystal composed of lithium, vanadium, and sulfur studied this time, vanadium forms a planar triangular lattice. Below the phase transition temperature, triangular motifs, formed by three adjacent vanadium atoms clustering together, appear throughout the triangular lattice. Associate Professor Katayama and his colleagues investigated the arrangement of vanadium above the phase transition temperature in detail using synchrotron radiation X-rays and electron beams. They found that zigzag chains of vanadium extending in various directions appeared randomly with a sub-micrometer scale spread. Furthermore, they determined that under electron beam irradiation, the direction and spatial extent of these zigzag chains changed on a timescale of seconds. This phenomenon, where the direction of the zigzag chains changes over time, is a characteristic feature of plastic crystals, a type of soft matter. This research points to a new direction for the development of functional materials, which could be called "inorganic plastic crystals."
The results of this research will be published in the online edition of *npj Quantum Materials*, a journal from the Nature portfolio, on February 18, 2021.
This research was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers JP20H02604, JP17K05530, JP19K14644, JP17K17793, JP20H01849, and JP19J10805. The synchrotron radiation experiments were conducted under shared use programs at SPring-8 and the Aichi Synchrotron Radiation Center.
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