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We employ synchrotron-based near-field infrared spectroscopy to image the phononic properties of ferroelectric domain walls in hexagonal (h) Lu0.6Sc0.4FeO3, and we compare our findings with a detailed symmetry analysis, lattice dynamics calculations, and prior models of domain-wall structure. Rather than metallic and atomically thin as observed in the rare-earth manganites, ferroelectric walls in h-Lu0.6Sc0.4FeO3 are broad and semiconducting, a finding that we attribute to the presence of an A-site substitution-induced intermediate phase that reduces strain and renders the interior of the domain wall nonpolar. Mixed Lu/Sc occupation on the A site also provides compositional heterogeneity over micron-sized length scales, and we leverage the fact that Lu and Sc cluster in different ratios to demonstrate that the spectral characteristics at the wall are robust even in different compositional regimes. This work opens the door to broadband imaging of physical and chemical heterogeneity in ferroics and represents an important step toward revealing the rich properties of these flexible defect states.

The successful theoretical prediction and experimental demonstration of hybrid improper ferroelectricity (HIF) provides a new pathway to couple octahedral rotations, ferroelectricity, and magnetism in complex materials. To enable technological applications, an HIF with a small coercive field is desirable. Sr3Sn2O7 single crystals are successfully grown, and it is discovered that they exhibit the smallest electric coercive field at room temperature among all known HIFs. Furthermore, it is demonstated that a small external stress can repeatedly erase and re‐generate ferroelastic domains. In addition, using in‐plane piezo‐response force microscopy, abundant charged and neutral domain walls are charaterized. The observed small electrical and mechanical coercive field values are in accordance with the results of the first‐principles calculations on Sr3Sn2O7, which show low energy barriers for both 90° and 180° polarization switching compared to those in other experimentally demonstrated HIFs. The findings represent an advancement towards the possible technological implemetation of functional HIFs. [ABSTRACT FROM AUTHOR]

Hybrid improper ferroelectricity, where an electrical polarization can be induced via a trilinear coupling to two nonpolar structural distortions of different symmetries, recently was demonstrated experimentally in the n=2 Ruddlesden-Popper compound Ca3Ti2O7. In this paper we use group theoretic methods and first-principles calculations to identify possible ferroelectric switching pathways in Ca3Ti2O7. We identify low-energy paths that reverse the polarization direction by switching via an orthorhombic twin domain or via an antipolar structure. We also introduce a chemically intuitive set of local order parameters to give insight into how these paths are relevant to ferroelectric switching nucleated at domain walls. Our findings suggest that switching may proceed via more than one mechanism in this material. [ABSTRACT FROM AUTHOR]

The successful theoretical prediction and experimental demonstration of hybrid improper ferroelectricity (HIF) provides a new pathway to couple octahedral rotations, ferroelectricity, and magnetism in complex materials. To enable technological applications, an HIF with a small coercive field is desirable. Sr3Sn2O7 single crystals are successfully grown, and it is discovered that they exhibit the smallest electric coercive field at room temperature among all known HIFs. Furthermore, it is demonstated that a small external stress can repeatedly erase and re‐generate ferroelastic domains. In addition, using in‐plane piezo‐response force microscopy, abundant charged and neutral domain walls are charaterized. The observed small electrical and mechanical coercive field values are in accordance with the results of the first‐principles calculations on Sr3Sn2O7, which show low energy barriers for both 90° and 180° polarization switching compared to those in other experimentally demonstrated HIFs. The findings represent an advancement towards the possible technological implemetation of functional HIFs. [ABSTRACT FROM AUTHOR]