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Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics

Abstract

Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling, are some of the most important functional materials, with applications ranging from ultrasound imaging to actuators. Since their discovery, their complex nanoscale chemical and structural heterogeneity has made the origins of their electromechanical properties extremely difficult to understand. Here, we employ aberration-corrected scanning transmission electron microscopy to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg1/3Nb2/3)O3–PbTiO3. We identify three main contributions that each depend on Ti content: chemical order, oxygen octahedral tilt and oxygen octahedral distortion. These heterogeneities are found to be spatially correlated with low-angle polar domain walls, indicating their role in disrupting long-range polarization and leading to nanoscale domain formation and the relaxor response. We further locate nanoscale regions of monoclinic-like distortion that correlate directly with Ti content and electromechanical performance. Through this approach, the connections between chemical heterogeneity, structural heterogeneity and local polarization are revealed, validating models that are needed to develop the next generation of relaxor ferroelectrics.

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Fig. 1: Atomic resolution polarization mapping.
Fig. 2: Distribution of structural and chemical heterogeneities.
Fig. 3: Correlation between atom column chemistry and the local distortion.
Fig. 4: Spatial relationship between domain walls and inhomogeneities.

Data availability

The image datasets analysed during the current study are available from https://doi.org/10.7910/DVN/F0FHTG. Other data is available from the corresponding author by reasonable request. Source data are provided with this paper.

Code availability

Custom Python scripts used to analyse STEM images are available from the corresponding author upon request.

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Acknowledgements

We thank the National Science Foundation for support for this work, as part of the Center for Dielectrics and Piezoelectrics under grant nos IIP-1841453 and IIP-1841466. S.Z. acknowledges support from the Australian Research Council (FT140100698) and the Office of Naval Research Global (N62909-18-12168). P.C.B. was supported by the Department of Defense through the National Defense Science and Engineering Graduate (NDSEG) fellowship programme. Computational time and financial support for J.N.B. was provided by AFOSR grant FA9550-17-1-0318. M.J.C. acknowledges support from the National Science Foundation as part of the NRT-SEAS under grant no. DGE-1633587. This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (ECCS-1542015). AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI). The NVIDIA Titan Xp GPU used for this research was donated by the NVIDIA Corporation. We thank M. Hauwiller for useful suggestions while preparing the manuscript.

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Contributions

A.K. conducted the electron microscopy experiments, data analysis and image simulations. M.J.C. prepared the PMN samples for electron microscopy and collected STEM data. S.Z. grew the PMN-xPT single crystals. J.N.B., P.C.B. and D.L.I. performed the DFT calculations and the corresponding analysis. J.M.L. and E.C.D. designed the electron microscopy experiments and guided the research. All authors co-wrote and edited the manuscript.

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Correspondence to James M. LeBeau.

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Supplementary Information

Sections 1–8, Figs. 1–15 and refs. 1–8.

Source data

Source Data Fig. 3

Normalized intensity of Mg/Nb/Ti sites, O–O distance along [110] (pm) and Pb/O–Pb/O distance along [001] (pm).

Source Data Fig. 4

The distance at which 95% of the heterogeneities are within that distance to a nearest domain wall, from experiment and the average of randomly generated datasets. The error bars represent the minimum and maximum 95% distances that were measured across all randomly generated datasets for each composition.

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Kumar, A., Baker, J.N., Bowes, P.C. et al. Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics. Nat. Mater. 20, 62–67 (2021). https://doi.org/10.1038/s41563-020-0794-5

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