High-Pressure Behaviors of Ag2S Nanosheets: An in Situ High-Pressure X-Ray Diffraction Research

Abstract

An in situ high-pressure X-ray diffraction study was performed on Ag2S 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 P21/n structure (phase I, α-Ag2S) to orthorhombic P212121 structure (phase II) at 8.9 GPa and then to monoclinic P21/n 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 Ag2S nanoparticles and bulk materials. Additionally, phase III was stable up to the highest pressure of 29.4 GPa. Bulk moduli of Ag2S 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 Ag2S nanoparticles. Further analysis suggested that the nanosize effect arising from the smaller thickness of Ag2S 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.

Ab initio Study of Atomic Structure and Electronic Properties of Different Phases of Polymorphic Ag2S

“…43(6) . This particular morph was observed for the tens of nanometer-size overlayers [23] and quantum dots [24] of similar characteristic sizes. Moreover, yet another monoclinic form of three-dimensional Ag 2 S was identified in Ref.…”

“…[22], it was shown that the nanocrystalline form of Ag 2 S has space group P2 1 /c ( Z = 4), and the following unit cell parameters were reported: a = 4.234(3) Å; b = 6.949(3) Å; c = 9.549(5) Å; and β = 125.43(6)°. This particular morph was observed for the tens of nanometer‐size overlayers [ 23 ] and quantum dots [ 24 ] of similar characteristic sizes. Moreover, yet another monoclinic form of three‐dimensional Ag 2 S was identified in Ref.…”

“…Moreover, at nanoscales, a monoclinic form of Ag 2 S with a = 4.214 Å, b = 6.912 Å, c = 7.853 Å, and β = 99.580° was identified in a recent study of Ref. [23] under ambient conditions, and some other P2 1 / n forms were observed under pressure.…”

“…Also, it was recently experimentally shown that under applied pressure structural transformations between different morphs take place, some of which retain P2 1 /c symmetry characteristic for the naturally occurring (mineral) form of Ag 2 S; i.e., the compound can undergo iso-symmetric phase transformations. [10,11] Moreover, by increasing the temperature above %173 K, the structure can be transformed into a cubic phase with extremely high ionic conductivity. [12] This extremely rich phase behavior allows for the properties tuning, while keeping stoichiometry the same.…”

Numerical simulation of quantum dots as a buffer layer in CIGS solar cells: a comparative study

“…Indeed, Ag 2 S QDs display presence of many strong diffraction peaks orientation along (110), (200), (211), (220), and (310) plane indicate the polycrystalline nature of films, which has been belong to the cubic phase, (JCPDS-00-001-1151). This can be explaining since Ag 2 S is stable in a monoclinic structure at room temperature, but suffers a thermo-induced phase shift into a cubic structure at 450 K 50 . Silver ions are randomly dispersed across the interstitial sites of a sulphur lattice in this high-temperature structure, resulting in a favourable ionic conductivity owing to the quantum effect of particle size.…”