Pb18O8Cl15I5: A Polar Lead Mixed Oxyhalide with Unprecedented Architecture and Excellent Infrared Nonlinear Optical Properties

To develop high-performance nonlinear optical (NLO) materials for infrared (IR) applications, we have applied a rational element-composition design strategy and investigated the unexplored PbO-PbCl2-PbI(2)system. By doing so, we discovered a new polar lead mixed oxyhalide, Pb18O8Cl15I5, the first synthetic metal oxyhalide combining both Cl(-)and I-. Pb(18)O(8)Cl(15)I(5)reveals an unprecedented structural feature with two different dimensional types of oxocentered Pb-O units, namely, [O4Pb8](8+)clusters and [OPb2](2+)chains. Centimeter-sized single crystals of Pb(18)O(8)Cl(15)I(5)have been successfully grown under ambient conditions. Remarkably, Pb(18)O(8)Cl(15)I(5)satisfies all fundamental yet rigorous criteria for high-performance IR NLO materials, exhibiting the widest IR transparency (up to 16.0 mu m) among oxide-based crystals, strong second-harmonic generation response (1.05xAgGaS(2)), superior birefringence (0.086 at 636 nm), and a high laser-induced damage threshold (8.5xAgGaS(2)).