Ba 2 ScBSi 2 O 9 : A Mixed-Coordination Borosilicate with a Low B/Si Ratio Exhibiting Enhanced Second Harmonic Generation Response.

Rational chemical substitution is an effective way to regulate structure and enrich property. Herein, a new noncentrosymmetric borosilicate, Ba 2 ScBSi 2 O 9 , was successfully synthesized by substituting CaO 6 units in Ba 2 CaB 2 Si 4 O 14 with ScO 6 octahedra, with comparatively strong covalency. This substitution not only effectively prevents polymerization of the B-O groups, resulting in an intriguing structural transformation from tetrahedral-coordinated borosilicate of Ba 2 CaB 2 Si 4 O 14 to mixed-coordinated borosilicate Ba 2 ScBSi 2 O 9 , but also enhances its second harmonic generation response (2 × KDP), that is nearly four times higher than its parent structure while keeping a short ultraviolet (UV) cutoff edge (λ cutoff < 190 nm). In addition, the polar space group of Pca 2 1 for Ba 2 ScBSi 2 O 9 achieves its ferroelectric polarization reversal capability, which makes quasi-phase-matching technology possible to counteract the nonphase-matching caused by small birefringence of silicates. This work indicates the unique role of heterovalent substitution in regulating structure and performance, providing new insights for exploring borosilicate with versatile functionality.