Different p-block elements induce C3[111] octahedral distortion in titanium to generate an intense nonlinear effect†

Abstract

Acentric crystalline materials are the cornerstone of numerous cutting-edge technologies and have been highly sought-after, but they are difficult to construct controllably. Herein, by introducing a new p-block element to break the symmetrical environment of the d⁰ transition metal in the centric matrix TiTe₃O₈, a novel acentric tellurite sulfate, namely Ti(TeO₃)(SO₄), was successfully constructed. In its structure, two types of p-block element-centered oxo-anionic groups, i.e. [TeO₃] and [SO₄], endow [TiO₆] with an out-of-center distortion along the local C₃[111] direction, which is rare in titanium oxides containing a lone-pair cation. The synergy of the distorted [TiO₆] octahedron, lone-pair [TeO₃] pyramid and rigid [SO₄] tetrahedron within its structure induces a strong second harmonic generation (SHG) response of 11.6 × KDP (KH₂PO₄), the largest value among mercury-free sulfates. Additionally, Ti(TeO₃)(SO₄) also shows the largest birefringence (0.145) among sulfates possessing an SHG response that is more than ten times that of KDP, showing huge potential as a nonlinear optical material. The successful implementation of the strategy of inducing intra-octahedral distortion in a d⁰ transition metal by different p-block elements provides new opportunities for constructing acentric structures and exploiting outstanding nonlinear optically active sulfates.