2018 Fiscal Year Final Research Report

Permittivity control due to dielectric tunable materials using ferroelectric critical endpoint

Research Project

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Project/Area Number	16K13820
Research Category	Grant-in-Aid for Challenging Exploratory Research
Allocation Type	Multi-year Fund
Research Field	Condensed matter physics I
Research Institution	Nagoya Institute of Technology
Principal Investigator	Iwata Makoto 名古屋工業大学, 工学(系)研究科(研究院), 教授 (40262886)
Co-Investigator(Kenkyū-buntansha)	籠宮功名古屋工業大学, 工学(系)研究科(研究院), 准教授 (40318811)
Project Period (FY)	2016-04-01 – 2019-03-31
Keywords	強誘電体 / 誘電率 / 誘電チューナビィティー / 電場誘起相転移 / 臨界点 / ペロブスカイト / 酸化物 / 構造相転移
Outline of Final Research Achievements	The dielectric tunable material is defined as a material changing the permittivity largely due to the DC electric field. To use such materials in the filter circuit of smartphones, the tunability higher than 90% is required. The applicants had already clarified both in experiment and theory that the large dielectric tunability appears if the material located near the ferroelectric critical endpoint is adopted. At that point, however, no material showing tunability higher than 90% at room temperature was found. In this research, materials were searched, and among them, Pb(Sc1/2Ta1/2)O3 (PST) single crystals were grown. It was found experimentally that the tunability in PST exceeds 90% at room temperature. Thus, the goal of this study was achieved.
Free Research Field	強誘電体構造相転移
Academic Significance and Societal Importance of the Research Achievements	これまでのチューナブル材料の探索では、ヒステリシスループの角型性が小さいソフト強誘電体材料やリラクサーや複合材料 (含人工超格子) のような非線形性の大きな不均一系材料が調べられてきたが、探索に指導原理が無く、経験則による研究が進められていた。申請者の知る限り、申請段階でt = 90% を越える材料は、まだ見つかっていなかった。本研究の学術的価値は、大きなチューナブル材料を探索するときには室温付近に強誘電的臨界点のある物質を探せばよいという探索指針を明らかにしたことであり、社会的価値は、PST を用いると、室温付近でチューナビリティーが90％を超えることを実験的に見出したことである。