Enhanced linear electro-optic effect in BaTiO3 nanocrystal films prepared by electrophoretic deposition

Electro-optic (EO) modulators are essential for high-speed optical communication and integrated photonic systems, yet the development of low-cost materials with strong Pockels activity remains a challenge. Barium titanate (BaTiO3, BTO) is a promising intrinsic EO material due to its large EO coefficient and a non-centrosymmetric crystal structure, but solution-processed BTO films often suffer from random nanocrystal orientation and poor density, which limit their effective EO performance. In this work, we demonstrate an electrophoretic deposition (EPD) strategy for fabricating BTO nanocrystal films with enhanced linear EO response. By driving charged nanocrystals toward the substrate in an applied electric field, EPD promotes dense film assembly and partial alignment of crystal dipoles along the field direction. X-ray diffraction and second-harmonic generation measurements confirm the preservation of the tetragonal, non-centrosymmetric phase with preferential c-axis orientation. EO characterization using a modified Teng–Man method reveals a high-frequency r33 of approximately 40 pm·V−1, which is ∼360 times greater than that of spin-coated BTO films and exceeds the value of LiNbO3 single crystals. These results demonstrate that EPD provides an effective, scalable, and low-cost approach to improve the macroscopic EO response of ferroelectric nanocrystal films, offering a promising pathway toward compact, high-efficiency EO devices compatible with integrated photonic platforms.