Topological Defects and Ferroelastic Twins in Ferroelectric Nanocrystals using Coherent X-Rays

Xiaowen Shi¹ and Edwin Fohtung ^1*



1 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th St, Troy, NY 12180, USA



* Correspondence: fohtue@rpi.edu



Topological defects (TDs) are at the heart of many intriguing phenomena in condensed-matter physics and materials sciences. Emergent functionalities emanating from topological defects-such as the ability of domain walls to host itinerant electrons—make them potential hosts for charge conductivity and superconductivity, as previously reported in twinned crystals of WO₃.

In this study, we utilized Bragg coherent Diffractive Imaging (BCDI) to capture ferroelastic twins in individual BaFe₁₂O₁₉ (BHF) [1,2] and BaTiO₃ (BTO) [3] crystals. BCDI is a lens-less diffractive imaging technique that relies on coherent properties of X-ray beams to resolve local deformation fields in individual nanocrystals from measured coherent diffraction intensity. We reconstructed the morphology and local displacement field of (200) planes of the nanocrystal. Our reconstructions identified ferroelastic domains with homogenous displacement fields separated by domain boundaries using a standard spectral clustering algorithm [4]. The efficacy of BCDI in studying TDs in three dimensions was thus demonstrated.



We have demonstrated that x-ray Bragg coherent diffractive imaging (BCDI) is a high-resolution probe capable of retrieval of the morphology, local displacement field and ferroelastic domains in a twinned magnetic ferroelectric nanocrystal. The interplay of ferroelastic twins and ferroelectric polarization will undoubtedly affect the performance and emergent functional properties in ferroelectric material systems. BCDI can be applied to a variety of soft and hard condensed-matter system to probe in operando processes.

With the intense development of the high-brilliance 4th generation synchrotron radiation facilities worldwide, the ultimate goal is to achieve diffraction-limited spatial resolution with versatile capabilities using BCDI to characterize nano-scale next-generation electronic devices and resolve unanswered questions in condensed-matter physics.