We obtained the number of S atoms surrounding Re, the Debye-Waller value, and the accurate Re-S bond length, which decreases from 2.413 Å at ambient pressure to 2.378 Å at 20.4 GPa by the local structural fitting analysis. The Fourier transformed results show that the Re-S bond lengths gradually become shorter as the pressure increases in the entire measurement range. We found an intralayer transition at 6.0 GPa, which was associated with the counterclockwise rotation of S atoms around the chain of Re atoms leading to the interlayer S-S covalentlike bond formation, followed by an interlayer transition from disordered to ordered stacking at 20.4 GPa. By in-situ high-pressure Extended X-ray Absorption Fine Structure (EXAFS) measurements, we investigated the local structure evolution of ReS₂. The results of high-pressure XAS also confirmed that CsPbBr₃ undergoes a phase transition at 1.2 GPa, and through the analysis of the Fourier transform results, we know that the pressure causes the Pb-Br distance to decrease continuously, resulting in the distortions and contractions of the PbBr6 octahedra, which induces the phase transition. By in situ high-pressure photoconductive measurements, we found that the visible light response of CsPbBr₃ in the second phase was significantly better than that of the ambient phase, indicating that pressure can improve its photoelectric properties. When the pressure exceeds 2.3 GPa, the ionic conduction disappears, and the transition from ion/electron mixed conduction to pure electronic conduction occurs. We found that CsPbBr₃ undergoes a structural phase transition at 1.2 GPa, and when the pressure is below 2.3 GPa, both electronic and ionic conduction coexist within CsPbBr₃. By in-situ high-pressure impedance spectroscopy measurements, we have systematically studied the electrical transport properties of CsPbBr₃. In these measurements, the detailed results of the study are as follows: 1.
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The structural evolution of these materials was investigated under pressure using in-situ X-ray absorption spectroscopy (XAS) method. The electrical transport properties of CsPbBr₃ were investigated under pressure by in-situ alternative current (AC) impedance spectroscopy and photocurrent measurements. In this work, we select CsPbBr₃, ReS₂, and black arsenic (bAs) as the research objects, which are representative of perovskite and two-dimensional materials. Pressure is an important means which can alter the geometric and electronic structures of the materials, thereby changing the electrical transport and photoelectric properties of the materials. Perovskite solar cell materials and two-dimensional layered materials have attracted worldwide attention as solar harvesting materials because of their remarkable photovoltaic properties. These results highlight the critical role of the atomic structure and interfacial interactions in shaping the stability and electronic characteristics of vdW layered materials, thus enabling a new degree of freedom to engineer their properties using scalable processes. Furthermore, the electronic structure of this intermediate phase is found to be determined by surface self-passivation and the associated competition between A7- and A17-like bonding in the bulk. At a critical thickness of ~4 nm, A17 antimony undergoes a diffusionless shuffle transition from AB to AA stacked alpha-antimonene followed by a gradual relaxation to the A7 bulk-like phase. This metastability of the A17 phase is revealed by real-time studies unraveling its thickness-driven transition to the A7 phase and the concomitant evolution of its electronic properties. Herein, we demonstrate that these two phases not only co-exist during the vdW growth of antimony on weakly interacting surfaces, but also undertake a spontaneous transformation from the A17 phase to the thermodynamically stable A7 phase. On the other hand, bulk heavier elements are only stable in the A7 phase.
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Light group VA elements are found in the layered orthorhombic A17 phase such as black phosphorus, and can transition to the layered rhombohedral A7 phase at high pressure. Pnictogens have multiple allotropic forms resulting from their ns2 np3 valence electronic configuration, making them the only elemental materials to crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout the group.