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

Ran Liu,Bo Liu,Bing-Bing Liu,Quan-Jun Li

doi:10.3390/nano10091640

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.

Highlights

As a well-known metal sulfide, Ag2S is a direct narrow band gap semiconductor (~1.5 eV), with high absorption coefficient (104 m−1), good chemical stability and optical properties [1,2,3]
Thereby, β-Ag2S is considered as a fast ionic conductor (FIC), which has potential applications including in energy, analytical chemistry, biomedicine, solid-state ionic devices and so forth [13,14,15]
We studied the high-pressure behaviors of Ag2S nanomaterials with sheet-like morphologies using in situ high-pressure X-ray diffraction up to about 30 GPa

Summary

Introduction

As a well-known metal sulfide, Ag2S is a direct narrow band gap semiconductor (~1.5 eV), with high absorption coefficient (104 m−1), good chemical stability and optical properties [1,2,3]. Ag2S materials have been extensively synthesized and studied due to their important applications including semiconductors, photovoltaic cells, infrared detectors, photoelectric switches and oxygen sensors [4,5,6]. While heating above 450 K, Ag2S undergoes a thermo-induced phase transition and reforms into a body-centered cubic (bcc) structure (β-Ag2S, space group Im3m) [8,9]. In this high-temperature structure, silver ions are randomly distributed over the interstitial sites of a bcc sulfur lattice [10,11], leading to a favorable ionic conductivity as high as 5 Ω−1 cm−1 [12]. At about 860 K, Ag2S further converse into a face-centered cubic (fcc) phase (γ-Ag2S), keeping stable up to melting temperature [9]

Methods

Results

Conclusion