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Pressure tuning the lattice and optical response of silver sulfide

Binary transition metal chalcogenides have attracted increasing attention for their unique structural and electronic properties. High pressure is powerful tool for tuning their crystal structure and electronic structure away from their pristine states.In this work, we systematically studied the in situ structural and optical behavior of silver sulfide (Ag2S) under pressure by X-ray diffraction (XRD) and Infrared (IR) spectroscopy measurements in a diamond anvil cell. Upon compression, Ag2S undergoes structural symmetrization from monoclinic to orthorhombic, represented by the decrease of angle from 99 to 90 degrees through a series of structural transitions coupled with lattice contractions. IR transmission and reflectivity measurements showed that pressure effectively tunes semiconducting Ag2S into a metal at ~ 22 GPa. Drude model analysis of the IR reflectivity indicates that the optical conductivity evolves significantly, reaching the highest conductivity at ~ 40 GPa. Our results highlight pressure's dramatic role in tuning the structural and electronic state of silver chacogenides.