ガラスにならない酸化アルミニウムを透明な非晶質の塊に ～5配位ピラミッドと6配位八面体から成る超高密度構造と結晶を超える誘電率を高圧力で実現～

2026-04-07 工学院大学

図 　本研究で合成した透明バルク非晶質アルミナの誘電率と構造

＜関連情報＞

• https://www.kogakuin.ac.jp/news/2026/040791.html
• https://pubs.acs.org/doi/10.1021/jacs.5c22344

バルク非晶質アルミナ：高誘電率を実現する五面体ピラミッドと八面体の密度駆動型相互作用 Bulk Amorphous Alumina: The Density-Driven Interplay of Pentahedral Pyramids and Octahedra for High Dielectric Permittivity

Hideki Hashimoto,Yohei Onodera,Rei Okuno,Masashi Miyakawa,Hitoshi Yusa,Takashi Taniguchi,Sho Kakizawa,Shuya Sato,Takao Shimizu,Taro Kuwano,Takato Abe,Naoki Takata,Dasom Kim,Koji Yazawa,Kenzo Deguchi,Shinobu Ohki,Koji Kimoto,Shunsuke Shimizu,Yuto Okawara,Yuta Nishina,Aiko Shimada,Ryuichi Maekawa,Koji Ohara,Yuta Shuseki,Hidetoshi Morita,Tomoko Sato,Hiroyo Segawa,Hiroki Taniguchi,Atsunobu Masuno,Takeharu Yoshii,Koji Kawada,Toshinori Okura,and Shinji Kohara
Journal of the American Chemical Society  Published: April 7, 2026
DOI:https://doi.org/10.1021/jacs.5c22344

Abstract

The synthesis of single-component oxide glasses, represented by Al₂O₃ (alumina), is an unexplored area because they have no glass-forming ability. We synthesized a transparent bulk amorphous alumina with excellent thermal conductivity, hardness, and dielectric permittivity by applying high pressure to an amorphous alumina porous thin film. We found that a pyramidal 5-fold polyhedron (AlO₅), which resembles a deformed octahedron without one oxygen vertex, is a principal structural unit in the amorphous alumina. The application of high pressure induces the formation of an edge-sharing matrix composed of further-deformed AlO₅ pyramids and increased AlO₆ octahedra, resulting in the improvement of the dielectric permittivity exceeding α-Al₂O₃. Our newly proposed synthesis method, which achieves an anomalous matrix formed by the density-driven interplay of pyramids and octahedra, has the potential to pave the way for the creation of a wide range of novel bulk amorphous materials without glass-forming ability, exhibiting excellent physicochemical properties.