Heterocationic strategy to design a nonlinear optical crystal with a polar anti-perovskite structure

The rational design of noncentrosymmetric (NCS) inorganic materials remains a longstanding challenge due to unpredictable solid-state reactions and stringent requirements on symmetry breaking. Although perovskites have been widely used as structural templates for NCS materials, their anti-perovskite counterparts remain unexplored. Here, by incorporating Cs⁺ and Cd²⁺ ions into a centrosymmetric Na₃Cl[MoO₄] template, we introduce a heterocationic strategy tailored for anion-centered anti-perovskites that, modifying the conventional BX₆ octahedra, yields the polar molybdate Cs₂NaCd₂Cl₃(MoO₄)₂. The heterocationic sublattice induces pronounced octahedral distortion, breaks inversion symmetry, and aligns the [MoO₄] tetrahedra, resulting in a wide band gap of 4.37 eV, a broad transparency window (0.26-5.42 μm and 6.25-10.46 μm), an SHG coefficient twenty times larger than KH₂PO₄ (d₁₅ = 9.31 pm/V) and a congruent-melting dynamics, enabling single-crystal growth. This work unveils the potential of heterocationic engineering in anion-centered frameworks demonstrating the design of NCS and polar functional materials with excellent nonlinear optical properties.