天美影视

A group led by Professor Yuzo Shigesato (Department of Chemistry and Biological Science, Graduate School of Science and Engineering Course in Functional Materials Science and Inorganic Materials Laboratory, Department of Science and Engineering) and Professor Tadashi Suzuki (Department of Chemistry and Biological Science, Graduate School of Science and Engineering Course in Chemistry and Physical Chemistry Laboratory, Department of Science and Engineering) has successfully elucidated the hydrogenation/dehydrogenation reaction mechanism of functional rare-earth thin films through joint research.

In the Inorganic Materials Laboratory, thin films of rare earth elements such as samarium (Sm), gadolinium (Gd), and yttrium (Y) with a thickness of several hundred nm have been studied as functional materials that can reversibly control light, electricity, and heat in a large range because of the metal/semiconductor phase change induced by the hydrogenation/dehydrogenation reaction using palladium (Pd) as catalyst. Therefore, they have been studied as functional materials that allow reversible control of light, electricity, and heat over a large range of temperatures. The chemical reaction mechanism of these reactions has not been elucidated, and the mechanism that determines the reaction rate has not been clarified.

In this study, the Inorganic Materials Laboratory and the Physical Chemistry Laboratory collaborated to conduct real-time in-situ analysis of various physical properties and succeeded in analyzing the detailed dependence of reaction rates on temperature for the first time in the world. This research result has been published in the "Japanese Journal of Applied Physics," an academic journal published by the Japan Society of Applied Physics.

Research members
Xu Gaibun (Formerly: Graduate School of Science and Engineering, Master's course in Shigesato Laboratory, Functional Materials Formation Course)
Min-Seok Kim (College of Science and Engineering Department of Chemistry and Biological Science Assistant Professor, Shigesato Laboratory)
Tadashi Suzuki（Graduate School of Science and Engineering Chemistry Course, Professor)
Yuzo Shigesato（Graduate School of Science and Engineering Professor, Course in Functional Materials Formation)

Title of paper
Temperature dependence of the hydro-/dehydrogenation reaction kinetics on SmH2 films.
Author(s).
Kaiwen Zhu, Minseok Kim, Tadashi Suzuki and Yuzo Shigesato
Journal of Applied Physics, Japanese Journal of Applied Physics, Japanese Journal of Applied Physics
Japanese Journal of Applied Physics, Volume 65, Number 7, 2026.
DOI 10.35848/1347-4065/ae56c4

Research overview

In certain rare earth elements, or alloys of transition metals and Mg, there are materials that undergo a phase change between metal and semiconductor through hydrogenation/dehydrogenation reactions when an ultrathin 5-10 nm Pd film is supported on the top surface as a catalyst. These are called photochromic mirror materials. Reversible hydrogenation/dehydrogenation reactions can be carried out in two ways: (1) gaschromic methods, which involve exposure to 3% hydrogen-containing nitrogen gas at 1 atmosphere (a safe hydrogen concentration below the explosion limit), and (2) electrochromic methods, which involve hydrogenation/dehydrogenation reactions by electrochemical H+ injection in an electrolyte. The Shigesato Laboratory has repeatedly deposited films using the sputtering method for many materials and has been exploring the optimal materials and thin film synthesis conditions for reversible hydrogenation/dehydrogenation reactions in both of these methods (1) and (2). However, the detailed mechanism of hydrogenation/dehydrogenation reactions using palladium catalysts has not been elucidated until now.

This time, we present our research results on the reaction (1) in Sm thin films. We demonstrated that the hydrogenation reaction can be explained by the Johnson–Mehl–Avrami-Kolmogorov (JMAK) model, a theoretical formula used for nucleation and crystal growth, and we elucidated the nucleation and growth mechanism of hydrides in the solid phase. Furthermore, we demonstrated that the dehydrogenation reaction mechanism is completely different and can be explained by the theoretical formula of diffusion (Fick's second law).

These studies are expected to lead to the design and control of the change rate of new devices that can simultaneously switch light transmittance, electrical conductivity, and thermal conductivity, as well as the realization of more stable and cycle-durable phase changes and improved reversibility.

Currently, we are conducting further detailed in-situ structural analysis of both reactions (1) and (2) using multimodal analysis with synchrotron radiation at the High Energy Accelerator Research Organization (KEK-PF).