Paradigm shift in ferroelectric materials research

2019 Fiscal Year Final Research Report

• Project/Area Number: 18K18940
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Kyoto University
• Principal Investigator: Fujita Koji 京都大学, 工学研究科, 教授 (50314240)
• Project Period (FY): 2018-06-29 – 2020-03-31
• Keywords: 強誘電体 / 圧電体

Outline of Final Research Achievements

Noncentrosymmetry in layered perovskites, which is induced by ubiquitous rotational/tilting distortions, offers an attractive route to the discovery of new ferroelectric or piezoelectric materials. In this study, we demonstrate inversion symmetry breaking induced by oxygen octahedral rotations in A-site-ordered n = 1 Ruddlesden-Popper (RP) KRTiO4 (R = rare earth) using a combined experimental and theoretical approach.
We also discover that n = 2 RP Sr3Zr2O7 and (Sr,Ca)3Sn2O7 are hybrid-improper ferroelectrics, whereby an electric polarization occurs by a combination of two nonpolar rotational modes via a trilinear coupling. We find that the Curie temperature increases linearly with increasing the Ca2+ content in (Sr,Ca)3Sn2O7, i.e., with decreasing the tolerance factor. Remarkably, this linear relationship is applicable to the suite of all known A3B2O7 hybrid improper ferroelectrics.

Free Research Field

無機材料化学

Academic Significance and Societal Importance of the Research Achievements

膨大なペロブスカイト化合物の中で強誘電体・圧電体は5%に満たず、応用分野も限定的であった。本研究で示した酸素八面体回転を利用した強誘電体・圧電体の物質設計では、元素選択の自由度が大きいため、物質探索により高機能な新規強誘電体・圧電体が登場する可能性は大いにある。また、現在は鉛を含むペロブスカイトPb(Zr,Ti)O3が圧電素子として広範に利用されているが、環境保全の観点からこれを代替する無鉛圧電材料の開発が強く求められている。酸素八面体回転による強誘電性・圧電性の発現はそのような産業界の要望にも応えることができる。