Bragg coherent diffractive imaging of polar domain structure in LiNbO3 thin films

We employ Bragg coherent diffractive imaging to reconstruct the three-dimensional [102] displacement field and strain within individual grains of ferroelectric LiNbO3 thin films. By directly imaging buried nanoscale ferroelastic and ferroelectric textures, this approach provides a nondestructive route to resolve internal electromechanical structure in technologically relevant oxide energy materials. Coherent diffraction around the (102) Bragg peak reveals twin-like features, despite classical deformation twinning being symmetry-forbidden in LiNbO3 by its R3c structure and absence of a {102} glide plane. Iterative phase retrieval achieves sub-20 nm spatial resolution, resolving inversion-type ferroelectric domains with domain-wall widths of ∼50–60 nm. Landau phase-field simulations of coupled polarization and strain reproduce the observed domain morphology and strain profiles. This combined experimental–theoretical framework establishes a nondestructive approach to probe nanoscale polarization–strain coupling, with direct implications for the design and optimization of ferroelectric thin films for electro-optic, piezoelectric, and energy-conversion applications.