Science and function exploration of improper ferroelectrics

2021 Fiscal Year Final Research Report

• Project/Area Number: 19H02433
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 26020:Inorganic materials and properties-related
• Research Institution: Kyoto University
• Principal Investigator: FUJITA Koji 京都大学, 工学研究科, 教授 (50314240)
• Co-Investigator(Kenkyū-buntansha): 村井 俊介 京都大学, 工学研究科, 助教 (20378805)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 強誘電体 / 圧電体

Outline of Final Research Achievements

Piezoelectricity and improper ferroelectricity in layered perovskites, which utilize ubiquitous rotation/tilting distortions to break inversion symmetry, offer an attractive route to the discovery of new functional materials because their activity derives from geometric rather than electronic origins. In this study, we demonstrate that a layered perovskite oxide, SrLa2Sc2O7, crystallizes in a polar orthorhombic symmetry (space group A21am) at room temperature. The switchable polarization indicative of ferroelectricity can be revealed in a plot of polarization versus electric field.
In addition, we show that layered perovskite oxides, AgRTiO4 (R: rare earth), adopt an acentric tetragonal structure at room temperature. Interestingly, these compounds exhibit biaxial negative thermal expansion. We ascribe the observed phenomenon to the interplay between the structural distortions that alter the octahedral connectivity and shape.

Free Research Field

無機材料科学

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。酸素八面体回転に基づく強誘電体・圧電体の物質設計では、元素選択の自由度が大きいため、この方向での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強誘電体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。新しい機構に基づく新材料の開発はそのような産業界の要望にも応えることができる。