Orientational control of [IO3] groups enables strong optical anisotropy and second-harmonic generation in noncentrosymmetric Pb(IO3)2.

Orientational regulation of anionic groups has been recognized as an effective strategy for enhancing optical anisotropy. In this work, a noncentrosymmetric Pb(IO3)2-P1 phase was identified by machine learning accelerated CALYPSO structure screening and investigated by first-principles calculations. Among all screened candidates, Pb(IO3)2-P1 was the lowest energy structure, and its dynamical stability was verified by the absence of imaginary phonon modes. It has an HSE06 bandgap of 3.33 eV, and a large birefringence of 0.269@1064 nm, together with a moderate effective SHG coefficient of 0.56 pm V-1 (≈ 1.71 × KDP). Electronic structure, real-space atom-cutting, and Born effective charge analyses reveal that its optical response originates from the cooperative interaction among I centered stereochemically active lone pairs, oriented [IO3] groups, and bridging O atoms. These results establish Pb(IO3)2-P1 as a promising birefringent iodate NLO candidate and highlight [IO3] orientational control as a useful route for enhancing optical anisotropy.