【公開日：2025.06.10】【最終更新日：2025.04.22】
課題データ / Project Data
課題番号 / Project Issue Number
24QS0022
利用課題名 / Title
Elucidating the mechanism of a photochromic effect in YOxH3-2x thin films using the PDF technique
利用した実施機関 / Support Institute
量子科学技術研究開発機構 / QST
機関外・機関内の利用 / External or Internal Use
外部利用/External Use
技術領域 / Technology Area
【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-
【重要技術領域 / Important Technology Area】（主 / Main）量子・電子制御により革新的な機能を発現するマテリアル/Materials using quantum and electronic control to perform innovative functions（副 / Sub）革新的なエネルギー変換を可能とするマテリアル/Materials enabling innovative energy conversion
キーワード / Keywords
thin films, atomic pair distribution function, local structure,X線回折/ X-ray diffraction,放射光/ Synchrotron radiation,水素貯蔵/ Hydrogen storage
利用者と利用形態 / User and Support Type
利用者名（課題申請者）/ User Name (Project Applicant)
Kim Hyunjeong
所属名 / Affiliation
産業技術総合研究所
共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes
榊 浩司,中平 夕貴
ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes
町田 晃彦
利用形態 / Support Type
（主 / Main）共同研究/Joint Research（副 / Sub）-
利用した主な設備 / Equipment Used in This Project
報告書データ / Report
概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)
RE-O-H thin films including Y-O-H thin films draw much attention due to their large reversible photochromic effect, i.e. transparent thin films become dark by UV illumination. Y-O-H thin films crystallize in an fcc structure similar to black metallic β-YH~2, but optical and electrical properties are similar to those of transparent semiconducting hcp γ-YH~3. Photochromism had been reported in hcp γ-YH~3 at extremely low temperature [1] and in the coexistent state of fcc β-YH~2 and hcp γ-YH~3 under very high pressure [2]. However, interestingly enough, photochromism in Y-O-H thin films occurs in ambient conditions, and they were initially considered as transparent γ-YH3 stabilized by oxygen. However, it was recently established that they are indeed oxyhydride YOxH3-2x thin films whose optical band gap can change by varying the anion ratio over a wide composition range along the REH3-RE2O3 line [3]. Their photochromic effect has been extensively studied because of their various possible technological applications, but the underlying mechanism of the photodarkening process has not been completely elucidated yet. It is suggested from Raman measurements that upon illumination the gradual formation of small metallic domains in the semiconducting lattice is responsible for the photodarkening of YOxH3-2x thin films [4]. However, direct experimental evidence for this unique structure and its details, such as the size of metallic domains and their lattice expansion are still missing.
実験 / Experimental
In this study, we have employed the atomic pair distribution function (PDF) technique to investigate the formation of metallic domains in YO0.5H2 thin film during UV illumination. The PDF is a local structural probing technique that gives the probability of finding atom pairs separated by distance r [5]. Total scattering experiment was carried out at the National Institutes for Quantum Science and Technology (QST) experimental station at the Japan Atomic Energy Agency (JAEA) beamline of BL22XU at SPring-8. An YO0.5H2 thin film was loaded in a flat sample holder and placed perpendicular to the incident x-ray beam. Data were collected at room temperature with and without UV illumination using a large amorphous silicon detector manufactured by Perkin Elmer. We also measured ground YO0.5H2 thin film loaded in a polyimide capillary with a diameter of 1.00 mm for comparison.
結果と考察 / Results and Discussion
It turns out that the YO0.5H2 thin film is textured and intensity of some of diffraction peaks is too small. As a result, it is difficult to directly fit structural models to the experimental PDFs. However, we have observed some structural changes by UV illumination. The most prominent change occurred in its lattice parameter: the lattice parameter of the YO0.5H2 thin film decreases slightly by UV illumination. Besides change in lattice parameter, change in PDFs was too small to analyze. However, we found that analyzing difference between two PDFs may provide us useful information related to its photochromic effect. Our preliminary analysis results suggest that the local atomic arrangement of YO0.5H2 thin film changes by UV illumination and we are currently making structural models to explain the changes in the PDF.
図・表・数式 / Figures, Tables and Equations
その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)
References
[1] A. F. T. Hoekstra et al., Phys. Rev. Lett. 2001, 86, 5349-5352.
[2] A. Ohmura et al., Appl. Phys. Lett. 2007, 91, 151904.
[3] S. Cornelius et al., J. Phys. Chem. Lett. 2019, 10, 1342-1348.
[4] J. Montero et al., Phys. Rev. B: Condens. Matter Mater. Phys. 2017, 95, 201301.
[5] T. Egami and S. J. L. Billinge, Underneath the Bragg Peaks: Structural Analysis of Complex Materials, Pergamon Press Elsevier, Oxford, England, 2003.
成果発表・成果利用 / Publication and Patents
論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)
口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.
特許 / Patents
特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件