Ae₃[TO₃][SnOQ₃] (Ae = Sr, Ba; T = Si, Ge; Q = S, Se) and Ba₃[CO₃][MQ₄] (M = Ge, Sn; Q = S, Se): Design and Syntheses of a Series of Heteroanionic Antiperovskite-Type Oxychalcogenides

The heteroanionic materials (HAMs) have attracted more and more attention because they can better balance the functional properties of materials. However, their rational structural design is still a great challenge. Here, by using the antiperovskite Ba₃S[GeS₄] as a template and calculating the tolerance factor (t) as a reference, eight heteroanionic oxychalcogenides with balanced properties were finally synthesized by a partially group-substitution method. Among them, Ba₃[CO₃][MQ₄] (M = Ge, Sn; Q = S, Se) are centrosymmetric (CS) crystals and realize optimization of band gaps and birefringence. For Ae₃[TO₃][SnOQ₃] (Ae = Sr, Ba; T = Si, Ge; Q = S, Se), thanks to the novel [TO₄SnQ₃] polyanionic groups for the regulation to the antiperovskite structures and the contributions to the nonlinear optical (NLO) properties, they achieve the structural transition from CS to noncentrosymmetry and accomplish an excellent balance among the critical performance parameters as the potential candidates for the infrared NLO materials, including phase-matchable behavior, wide band gaps (E_g = 3.26–3.95 eV), high laser damage threshold (LDT = 3.2–4.4 × AgGaS₂), suitable birefringence (Δn = 0.065–0.098@2090 nm) and sufficiently strong second-harmonic generation responses (about 0.6–0.9 × AgGaS₂). Moreover, benefiting from crystallization in the polar space groups, they exhibit ferroelectricity and piezoelectricity at room temperature. As far as we know, this is the first reported fully inorganic antiperovskite ferroelectric. These demonstrate that our strategy is desirable and can provide some unique insights into the development of HAMs or antiperovskite materials with specific functions or structures.