A New Infrared Nonlinear Optical Crystal Ba ₅ Zn ₃ Ga ₂ Sn ₂ Se ₁₅ with Congruent Melting Behavior Based on Mixed-Metal T2-Supertetrahedral Units

Developing infrared nonlinear optical (NLO) crystals with practical application potential remains a great challenge. Here, by harnessing a hybrid supertetrahedral assembly strategy, we discovered a new infrared nonlinear optical material, Ba 5 Zn 3 Ga 2 Sn 2 Se 15, which crystallizes in the orthorhombic space group Ama 2. Its structure is based on the assembly of hybrid T2-type supertetrahedral clusters, forming a three-dimensional anionic framework built from one-dimensional hybrid [SnZn 3 Se 9 ] supertetrahedral chains and two-dimensional [SnGa 2 Se 8 ] anionic layers. This multicationic framework gives rise to the following properties: a phase-matchable SHG response of 1.3 × AgGaS 2, an experimental band gap of 2.27 eV, and a birefringence of 0.1055 at 1064 nm, which is sufficient for phase matching. Theoretical calculations indicate that the SHG response originates from distorted hybrid supertetrahedral units and asymmetric charge transfer along the M–Se bonds (M = Zn, Ga, Sn). The compound also exhibits congruent melting behavior, a prerequisite for growing large single crystals. This work suggests that hybrid supertetrahedral architectures are a viable platform for mid-infrared NLO materials.