Potassium-Stabilized 2H-Type Indium Sulfide in the Noncentrosymmetric Crystal K _0.33 [Zn _0.33 In _1.67 S ₃ ] Probed by Azimuthal SHG

High Resolution Image Download MS PowerPoint Slide K 0.33 Zn 0.33 In 1.67 S 3 ( KZIS ) material adopts a previously unreported layered structure in the indium sulfide family, featuring a layer topology analogous to the quintuple layer of α-phase In 2 Se 3 . This highly anisotropic structure, stabilized by defective cationic K + layers, crystallizes in the noncentrosymmetric space group P 6̅2 c with a = 3.8449(1) Å and c = 41.6818(6) Å through a synergistic analysis of single-crystal and synchrotron powder X-ray diffraction data. The Raman spectrum recorded from the plate-like crystal displays an intensive and sharp peak at a lower energy of 132 cm –1, indicative of pronounced out-of-plane vibrational characteristics typical of van der Waals layered materials. Owing to its wide band gap of 2.5 eV, KZIS exhibits a high laser-induced damage threshold (LIDT), about 6.3 times higher than that of the benchmark AgGaSe 2, highlighting its suitability for second-harmonic generation in two-dimensional systems. Furthermore, azimuthal second-harmonic generation (AZSHG) is performed on the (001) crystal surface (<100 μm) to probe the surface optical response. The results reveal weak but well-defined 6-fold rotational patterns under both parallel and perpendicular polarization electric fields, consistent with nonzero second-order susceptibility tensors allowed by the 6̅ m 2 point group.