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

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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.

Original languageEnglish
Article number4927
JournalNature Communications
Volume13
Issue number1
DOIs
StatePublished - Dec 2022

Funding

N.A. and L.M. acknowledge the support by NSF through the Pennsylvania State University Materials Research Science and Engineering Center (MRSEC) DMR-2011839 (2020–2026). Crystal growth at Rutgers was supported by the center for Quantum Materials Synthesis (cQMS), funded by the Gordon and Betty Moore Foundation’s EPiQS initiative through grant GBMF10104, and by Rutgers University. K.H. and E.A.N. acknowledge support from University of California, Merced. L.M. and P.M. acknowledge support from NSF DMR-1420620. We acknowledge the use of computational resources provided by the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. ACI-1548562, as well as the Multi-Environment Computer for Exploration and Discovery (MERCED) cluster at University of California, Merced, which is supported by National Science Foundation Grant No. ACI-1429783. D.M. was supported by ORNL’s Laboratory Directed Research and Development (LDRD) Program, which is managed by UT-Battelle, LLC, for the U.S. Department of Energy (DOE) under the contract no. DE-AC05-00OR22725. We appreciate the help from Dr. Rongwei Hu with crystals growth and Dr. Fei-Ting Huang for insightful discussions. We appreciate the insight and suggestion from Prof. Venkatraman Gopalan. We appreciate the support and resources from Materials Characterization Lab (MCL) at Penn State.

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