Synthesis, crystal growth, electronic properties and optical properties of Y${}_6$IV${}_{2.5}$S${}_{14}$ (IV=Si, Ge)

Two isostructural ternary acentric sulfides, Y${}_6$Si${}_{2.5}$S${}_{14}$ (1) and Y${}_6$Ge${}_{2.5}$S${}_{14}$ (2) were re-investigated to understand the origin of the chemical flexibility of RE${}_6$B${}_x$C${}_y$Ch${}_{14}$(RE=Y, La- Lu; B=Si, Ge, Sn, Al, Ga; C=monovalent M${}^{+}$ (Ag, Na, Li, etc.), divalent M${}^{2+}$ (Mg, Cr, Ni, Zn, etc.), trivalent M${}^{3+}$ (Al, In, Ga, etc.), tetravalent M${}^{4+}$ (Si, Ge, Sn) and pentavalent M${}^{5+}$ (Sb), Ch=S, Se), which consists of ∼ 444 isostructural compounds. Y${}_6$IV${}_{2.5}$S${}_{14}$ (IV=Si, Ge) were synthesized by a high-temperature salt flux method. The crystal structures of Y${}_6$IV${}_{2.5}$S${}_{14}$ (IV=Si, Ge) are constructed by [YS_8] polyhedra, [Si1S_6] octahedra, and [Si2S${}_4$] tetrahedra. The Si1 atom displaces from the center of [Si1S_6] octahedra with partial occupancy, which can be replaced by various metals, and mainly accounts for the chemical flexibility of the RE${}_6$B${}_x$C${}_y$Ch${}_{14}$ family. The bonding pictures of Y${}_6$Si${}_{2.5}$S${}_{14}$ were studied by electron localization function (ELF) and crystal orbital Hamilton population (COHP) calculations. Y${}_6$Si${}_{2.5}$S${}_{14}$ is evaluated as an indirect semiconductor with a bandgap of 2.4(1) eV measured by UV-Vis. The indirect bandgap of Y${}_6$Ge${}_{2.5}$S${}_{14}$ is 1.7(1) eV. Y${}_6$IV${}_{2.5}$S${}_{14}$ (IV=Si, Ge) are not type-I phase-matchable materials. For samples of 47 µm particle size, Y${}_6$Si${}_{2.5}$S${}_{14}$ and Y${}_6$Ge${}_{2.5}$S${}_{14}$ own good second harmonic generation (SHG) responses of ∼3.0×AGS and ∼2.8×AGS respectively. Y${}_6$Si${}_{2.5}$S${}_{14}$ and Y${}_6$Ge${}_{2.5}$S${}_{14}$ possess high laser damage threshold (LDT) of ∼5.5×AGS and ∼5.2×AGS respectively. (© 2021 Wiley‐VCH GmbH)