High-Pressure Behaviors of AgS Nanosheets: An in Situ High-Pressure X-Ray Diffraction Research.

An in situ high-pressure X-ray diffraction study was performed on AgS nanosheets, with an average lateral size of 29 nm and a relatively thin thickness. Based on the experimental data, we demonstrated that under high pressure, the samples experienced two different high-pressure structural phase transitions up to 29.4 GPa: from monoclinic 2/ structure (phase I, -AgS) to orthorhombic 222 structure (phase II) at 8.9 GPa and then to monoclinic 2/ structure (phase III) at 12.4 GPa. The critical phase transition pressures for phase II and phase III are approximately 2-3 GPa higher than that of 30 nm AgS nanoparticles and bulk materials. Additionally, phase III was stable up to the highest pressure of 29.4 GPa. Bulk moduli of AgS nanosheets were obtained as 73(6) GPa for phase I and 141(4) GPa for phase III, which indicate that the samples are more difficult to compress than their bulk counterparts and some other reported AgS nanoparticles. Further analysis suggested that the nanosize effect arising from the smaller thickness of AgS nanosheets restricts the relative position slip of the interlayer atoms during the compression, which leads to the enhancing of phase stabilities and the elevating of bulk moduli.