Hybrid improper ferroelectrics: design of ferroelectrics without second-order Jahn-Teller ions

2017 Fiscal Year Final Research Report

• Project/Area Number: 16K14386
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Inorganic materials/Physical properties
• Research Institution: Kyoto University
• Principal Investigator: Fujita Koji 京都大学, 工学研究科, 教授 (50314240)
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: 強誘電体

Outline of Final Research Achievements

In contrast to polar cation displacements driving oxides into noncentrosymmetric and ferroelectric states, inversion-preserving oxide anion displacements, such as rotations or tilts of oxygen octahedra about cation coordination centers, are exceedingly common. More than one nonpolar rotational mode in layered perovskites can lift inversion symmetry and combine to induce an electric polarization through a hybrid improper ferroelectric (HIF) mechanism. In this study, we report the new Ruddlesden-Popper HIF Sr3Zr2O7, which is the first ternary lead-free zirconate ferroelectric, and demonstrate room-temperature polarization switching. Our experimental and first-principles study shows that the paraelectric polymorph competes with the polar phase and emerges from a trilinear coupling of rotation and tilt modes interacting with an antipolar mode. Our work establishes the importance of understanding anharmonic interactions among lattice degrees of freedom.

Free Research Field

工学