Synthesis and Characterization of Mid-Infrared Transparency
Compounds: Acentric BaHgS<sub>2</sub> and Centric Ba<sub>8</sub>Hg<sub>4</sub>S<sub>5</sub>Se<sub>7</sub>
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Abstract
Two
mid-IR transparency compounds, namely, acentric BaHgS<sub>2</sub> (BHS)
and centric Ba<sub>8</sub>Hg<sub>4</sub>S<sub>5</sub>Se<sub>7</sub> (BHSSe), were successfully synthesized by a conventional
solid-state reaction method. The space group of BHS is orthorhombic <i>Pmc</i>2<sub>1</sub> with [HgS<sub>4</sub>] tetrahedra and isolated
dumbbell-shaped [HgS<sub>2</sub>] units, while BHSSe belongs to the
orthorhombic space group <i>Pnma</i> with infinite isolated <sub>∞</sub>[HgSe<sub>2</sub>(S/Se)<sub>2</sub>]<sup>4–</sup> chains. Raman spectra and thermal analysis of the titled materials
were measured. In addition, their band gaps are found to be 1.93 (BHS)
and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra.
Significantly, the powder BHS sample exhibits a good second harmonic
generation (SHG) response of ∼6.5 times compared with that
of reference AgGaS<sub>2</sub> at a fundamental wavelength (2.09 μm).
The calculated SHG coefficients of BHS are also reported, and the
maximum result agrees well with the test observation
