Atomic-Scale Displacement in Ordered SmMnO ₃ Nanoislands

In orthorhombic RMnO 3, multiferroicity is governed by epitaxial strain, which establishes a delicate balance between competing magnetic and ferroelectric interactions by tuning the Mn–O–Mn bond angles and Mn–O bond lengths. Here, we employed high-angle annular dark field (HAADF), atomic-resolution energy-dispersive X-ray spectroscopy (EDS), and annular bright field (ABF) imaging to resolve the structure of SmMnO 3 nanoislands grown on SrTiO 3 (001) by sol–gel spin coating. We quantified lattice constants, strain gradients, and unit-cell level polar displacements, finding polar displacements ranging from 4.26 to 20.47 pm with a marked reduction at the interface. Subunit-cell scale measurements showed Mn–O bonds shorten and Mn–O–Mn angles enlarge under ∼−3.5% in-plane compression. Electron energy loss spectroscopy (EELS) further reveals a uniform distribution of oxygen vacancies and a mixed Mn 3+ /Mn 2+ valence state with a constant L 3 /L 2 intensity ratio of ∼3.5 across the entire nanoisland. These atomic-scale measurements provide fundamental insights into the structure–property relationships governing structural polar behavior, offering valuable guidance for future functional applications.