Tailoring a Solar-Blind Ultraviolet Ferroelectric for Nonlinear Optics Through a Local Symmetry-Breaking Cascaded Strategy.

Solar-blind ultraviolet ferroelectrics are emerging as promising nonlinear optical candidates based on the quasi-phase matching principle. However, their development is hindered by the stringent symmetry requirements and the intrinsic coupling between polarization mechanisms and electronic structures. In this study, we propose a local symmetry-breaking cascaded strategy, in which molecular-level asymmetry is transmitted and amplified within a coordination framework to generate macroscopic ferroelectric polarization. Guided by this strategy, a new ferroelectric crystal, NH3CH2COO∙Li2SeO4, is obtained with the intrinsic asymmetry of glycine transmitted and amplified by high-symmetry tetrahedral groups and small-radius cations. This crystal exhibits a short ultraviolet cutoff edge (216 nm) and typical ferroelectricity (remanent polarization ∼ 8.4 µC/cm2, coercive field ∼ 18.8 kV/cm). Importantly, it further achieves the 266 nm output, validating its potential for solar-blind ultraviolet nonlinear optical applications. Structural analysis and ferroelectric characterization reveal that the macroscopic polarization originates from local symmetry breaking of glycine units, which is transmitted and amplified through the Li-SeO4 coordination network. This mechanism provides a generalizable design principle for discovering ultraviolet ferroelectrics, opening a promising avenue toward high-performance solar-blind ultraviolet nonlinear optical materials.