Crystal Structure, Electronic Structure, and Optical Properties of the Novel Li4cdge2s7, a Wide-Bandgap Quaternary Sulfide with a Polar Structure Derived from Lonsdaleite

Author

Andrew J. Craig
Seung Han Shin
Jeong Bin Cho
Srikanth Balijapelly
Jordan C. Kelly
Stanislav S. Stoyko
Amitava Choudhury, Missouri University of Science and TechnologyFollow
Joon I. Jang
Jennifer A. Aitken
A. Sarjeant

Abstract

The novel quaternary thiogermanate Li₄CdGe₂S₇ (tetralithium cadmium digermanium heptasulfide) was discovered from a solid-state reaction at 750 °C. Single-crystal X-ray diffraction data were collected and used to solve and refine the structure. Li₄CdGe₂S₇ is a member of the small, but growing, class of I₄-II-IV₂-VI₇ diamond-like materials. The compound adopts the Cu₅Si₂S₇ structure type, which is a derivative of lonsdaleite. Crystallizing in the polar space group Cc, Li₄CdGe₂S₇ contains 14 crystallographically unique ions, all residing on general positions. Like all diamond-like structures, the compound is built of corner-sharing tetrahedral units that create a relatively dense three-dimensional assembly. The title compound is the major phase of the reaction product, as evidenced by powder X-ray diffraction and optical diffuse reflectance spectroscopy. While the compound exhibits a second-harmonic generation (SHG) response comparable to that of the AgGaS₂ (AGS) reference material in the IR region, its laser-induced damage threshold (LIDT) is over an order of magnitude greater than AGS for λ = 1.064 μm and τ = 30 ps. Bond valence sums, global instability index, minimum bounding ellipsoid (MBE) analysis, and electronic structure calculations using density functional theory (DFT) were used to further evaluate the crystal structure and electronic structure of the compound and provide a comparison with the analogous I₂-II-IV-VI₄ diamond-like compound Li₂CdGeS₄. Li₄CdGe₂S₇ appears to be a better IR nonlinear optical (NLO) candidate than Li₂CdGeS₄ and one of the most promising contenders to date. The exceptional LIDT is likely due, at least in part, to the wider optical bandgap of ∼3.6 eV.

Recommended Citation

A. J. Craig and S. H. Shin and J. B. Cho and S. Balijapelly and J. C. Kelly and S. S. Stoyko and A. Choudhury and J. I. Jang and J. A. Aitken and A. Sarjeant, "Crystal Structure, Electronic Structure, and Optical Properties of the Novel Li4cdge2s7, a Wide-Bandgap Quaternary Sulfide with a Polar Structure Derived from Lonsdaleite," Acta Crystallographica Section C: Structural Chemistry, vol. 78, no. Pt 9, pp. 470 - 480, International Union of Crystallography; Wiley, Sep 2022.

The definitive version is available at https://doi.org/10.1107/S2053229622008014

Department(s)

Chemistry

Comments

National Science Foundation, Grant None

Keywords and Phrases

crystal structure; diamond-like; lonsdaleite; quaternary sulfide; thiogermanate; wide bandgap

International Standard Serial Number (ISSN)

2053-2296

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2023 The Authors, All rights reserved.

Publication Date

01 Sep 2022

PubMed ID

36063374