Tunable ferroelectricity in oxygen-deficient perovskites with Grenier structure 

Yongjin Shin & Giulia Galli 

npj Computational Materials  9: 218 (2023).

Editorial Summary

Ferroelectric materials have found many interesting applications in electronic and memory devices, and understanding and engineering their properties is a topic of great interest in condensed matter physics and materials science. Ferroelectricity can be realized in materials with broken spatial inversion symmetry. The formation of long-ordered oxygen vacancies in ABO3 perovskite oxides along specific crystal directions will cause the transformation of BO6 octahedral units into BO4 tetrahedral chains, which is expected to generate polarization through special twist. Among oxygen-deficient perovskites (ABO3−δ), δ is much smaller in the so-called Grenier phase (δ=1/3) than brownmillerites (δ=0.5). Recent experiments showed a spontaneous polarization coexisting with antiferromagnetism in R1.2Ba1.2Ca0.6Fe3O8 (R= Gd, Tb), pointing at the possibility of realizing stable polar Grenier phases. However, the relevant studies about the polarization of Grenier phases are quite rare. In this work, a group led by Prof. Giulia Galli from the Pritzker School of Molecular Engineering, University of Chicago, used using the first principles calculations to predict tunable ferroelectricity in oxygen-deficient RA2Fe3O8 perovskites with ordered oxygen vacancies,. They found that ferroelectricity can arise from cooperative distortions of octahedral and tetrahedral units, and larger cations combined with small R elements would lead to a maximum in the polarization and to a minimum in the FE switching barriers. They suggested that Grenier phase perovskites may be a promising platform to study the symmetry breaking phenomenon, which is expected to have a wide range of applications in magnetoelectric and non-volatile devices.  

编辑概述

铁电材料在电子和存储器件中有许多有趣的应用，理解和调控其性质是凝聚态物理和材料科学中一个非常有趣的课题。铁电可以在空间反转对称断破缺的材料中实现。在ABO₃钙钛矿氧化物中，沿着特定晶体方向形成具有长程有序的氧空位，将会导致BO₆八面体转变成BO₄链，从而有望通过特殊的转动产生极化。在缺氧钙钛矿（ABO_3-δ）中，格雷尼尔相的缺氧程度（δ= 1/3）要比褐磨钛矿的小（δ= 0.5）。最近有实验指出，极化与反铁磁在R_1.2Ba_1.2Ca_0.6Fe₃O₈ (R= Gd, Tb)中可以共存，表明了格雷尼尔相中实现铁电极化的可能性，但是相关的铁电极化研究极少。在本工作中，来自芝加哥大学普利兹克分子工程学院的Giulia Galli教授课题组，利用第一性原理预测了缺氧的RA₂Fe₃O₈钙钛矿中可以实现可调控的铁电性。他们发现，铁电产生于八面体和四面体单元之间的协同畸变，并且较大的A位碱土金属以及较小的R为稀土元素，可以使得极化变得最大并且让极化翻转的势垒变得最小。他们认为格雷尼尔相钙钛矿可能是一个研究对称性破缺现象的平台，有望在磁电耦合器件、非易失性存储器件等方面产生广泛的应用。