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Title: Li 2 Mg 2 Si 2 S 6 and Li 2 Mg 2 Ge 2 S 6 : Two nonlinear optical sulfides featuring a unique, polar trigonal structure incorporating ethane‐like anions

The new compounds Li2Mg2Si2S6and Li2Mg2Ge2S6have been prepared via traditional high‐temperature, solid‐state synthesis. The title compounds crystallize in the polar, noncentrosymmetric, trigonal space groupP31m(No. 157) and adopt a new structure type featuring staggered, ethane‐like (T2S6)6−units, where T=Si or Ge. These (T2S6)6−units are nestled within the holes of magnesium‐sulfide “layers” that are created through the edge‐sharing of MgS6octahedra. The holes found in the lithium‐sulfide “layers”, created by LiS6edge‐sharing octahedra, remain vacant, containing no (T2S6)6−anionic group. Through the face sharing of the respective MgS6and LiS6octahedra, the magnesium‐sulfide and lithium‐sulfide “layers” are stitched together resulting in an overall three‐dimensional structure. The optical bandgaps of Li2Mg2Si2S6and Li2Mg2Ge2S6are 3.24 and 3.18 eV, respectively, as estimated from optical diffuse reflectance UV‐Vis‐NIR spectroscopy. The compounds exhibit second harmonic generation responses of ∼0.24×KDP and ∼2.92×α‐quartz for Li2Mg2Si2S6and ∼0.17×KDP and ∼2.08×α‐quartz for Li2Mg2Ge2S6, using a Nd:YAG laser at 1.064 μm. Electronic structure calculations were performed using density functional theory and the linearized augmented plane‐wave approach within the WIEN2k software package. Examination of the electronic band structures shows that these compounds are indirect bandgap semiconductors.

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Author(s) / Creator(s):
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Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Zeitschrift für anorganische und allgemeine Chemie
Medium: X
Sponsoring Org:
National Science Foundation
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