2022-09-08 ペンシルベニア州立大学(PennState)
強い圧電特性を持つ、鉛フリー材料への道筋を開発するために、研究チームは、マンガン酸カルシウム、Ca3Mn2O7（CMO）に取り組んだ。
CMOのは、室温では、結晶の中に極性相と非極性相が共存している。
研究者達は、CMOの構造をより良く理解するために、原子スケールの透過型電子顕微鏡を使った。
＜関連情報＞
- https://www.psu.edu/news/materials-research-institute/story/unique-ferroelectric-microstructure-revealed-first-time/
- https://www.nature.com/articles/s41467-022-32090-w
(Ca, Sr)3Mn2O7における二重層極性ナノ領域とMnアンチサイトの研究 Double-Bilayer polar nanoregions and Mn antisites in (Ca, Sr)3Mn2O7
Leixin Miao,Kishwar-E Hasin,Parivash Moradifar,Debangshu Mukherjee,Ke Wang,Sang-Wook Cheong,Elizabeth A. Nowadnick & Nasim Alem
Nature Communications Published:22 August 2022
DOI:https://doi.org/10.1038/s41467-022-32090-w
Abstract
The layered perovskite Ca3Mn2O7 (CMO) is a hybrid improper ferroelectric candidate proposed for room temperature multiferroicity, which also displays negative thermal expansion behavior due to a competition between coexisting polar and nonpolar phases. However, little is known about the atomic-scale structure of the polar/nonpolar phase coexistence or the underlying physics of its formation and transition. In this work, we report the direct observation of double bilayer polar nanoregions (db-PNRs) in Ca2.9Sr0.1Mn2O7 using aberration-corrected scanning transmission electron microscopy (S/TEM). In-situ TEM heating experiments show that the db-PNRs can exist up to 650 °C. Electron energy loss spectroscopy (EELS) studies coupled with first-principles calculations demonstrate that the stabilization mechanism of the db-PNRs is directly related to an Mn oxidation state change (from 4+ to 2+), which is linked to the presence of Mn antisite defects. These findings open the door to manipulating phase coexistence and achieving exotic properties in hybrid improper ferroelectric.
