Non-centrosymmetric Structures Designed Rationally by “Dimensionality Addition” Strategy toward Promising Nonlinear Optical Family [A-X][In-Se] (A = K/Ba, Rb/Ba; X = Cl, Br)

Abstract

Formulating a well-defined strategy for designing non-centrosymmetric (NCS) structures is urgent but formidable challenge. Herein, we have conducted an all-around statistic of tetrahedra-based chalcogenides system, revealing a significantly high probability of obtaining NCS structures in rigid three-dimensional (3D) systems where the arrangement of tetrahedra units is minimally influenced by the non-directional spherical coordination of electropositive cations. Based on this premise, the “dimensionality addition” strategy implemented by regulating the A/M ratio (A = electropositive cations and M = tetrahedrally coordinated cations) is firstly established. By executing this strategy, six 3D NCS salt-inclusion selenides are successfully synthesized, namely A[A4Cl][In14Se23] (A = K, Rb), A2[A3BaCl][In18Se30] (A = K, Rb), and [K4Cl][AK9~10Cl4][In22Se38] (A = Li, Ba). All these compounds collectively employ separated polycations as “dimension regulator” to facilitate the assembly of [InSe4] tetrahedra into 3D NCS diamond-like frameworks, enabling promising second-harmonic generation (SHG) responses (0.69–2.10 × AgGaS2). This study may serve as instructive guidance for exploring symmetry-dependent materials.