Negative linear compressibility and structural stability of the energetic material -hexanitrostilbene under pressure.

The structural stability of the energetic material 2,2',4,4',6,6'-hexanitrostilbene (-HNS) under high pressure is critical for optimizing its detonation performance and low sensitivity. However, its structural response to external pressure has not been sufficiently investigated. In this study, high-pressure single-crystal X-ray diffraction data of -HNS demonstrate that the sample exhibits pronounced anisotropic strain, demonstrating an unusual negative linear compressibility (NLC) along the axis, with a coefficient of -4.

Revisiting the High-Pressure Behaviors of Zirconium: Nonhydrostaticity Promoting the Phase Transitions and Absence of the Isostructural Phase Transition in -Zirconium.

Zirconium (Zr) is an important industrial metal that is widely used in nuclear engineering, chemical engineering, and space and aeronautic engineering because of its unique properties. The high-pressure behaviors of Zr have been widely investigated in the past several decades. However, the controversies still remain in terms of the phase transition (PT) pressures and the isostructural PT in β-Zr: why the PT pressure in Zr is so scattered, and whether the β to β' PT exists.

Interplay of Anionic Quasi-Atoms and Interstitial Point Defects in Electrides: Abnormal Interstice Occupation and Colossal Charge State of Point Defects in Dense fcc-Lithium.

Electrides are an emerging class of materials with highly localized electrons in the interstices of a crystal that behave as anions. The presence of these unusual interstitial quasi-atom (ISQ) electrons leads to interesting physical and chemical properties and wide potential applications for this new class of materials. Crystal defects often have a crucial influence on the properties of materials.

Temperature- and Rate-Dependent Pathways in Formation of Metastable Silicon Phases under Rapid Decompression.

High-pressure metallic β-Sn silicon (Si-II), depending on temperature, decompression rate, stress, etc., may transform to diverse metastable forms with promising semiconducting properties under decompression. However, the underlying mechanisms governing the different transformation paths are not well understood.

Reciprocating Compression of ZnO Probed by X-ray Diffraction: The Size Effect on Structural Properties under High Pressure.

Zinc oxide, ZnO, an important technologically relevant binary compound, was investigated by reciprocating compress the sample in a diamond anvil cell using in situ high-pressure synchrotron X-ray diffraction at room temperature. The starting sample (∼200 nm) was compressed to 20 GPa and then decompressed to ambient condition. The quenched sample, with average grain size ∼10 nm, was recompressed to 20 GPa and then released to ambient condition.

High-Pressure Effects on Hofmann-Type Clathrates: Promoted Release and Restricted Insertion of Guest Molecules.

The search for effective methods to accurately control host-guest relationship is the central theme of host-guest chemistry. In this work, high pressure successfully promotes guest release in the Hofmann-type clathrate of [Ni(NH)Ni(CN)]·2CH (Ni-Bz) and restricts guest insertion into Ni(NH)Ni(CN) (Ni-Ni). Because of the weak host-guest interactions of Ni-Bz, external force gradually removes guest benzene from the host framework, leading to puckered layers.

High-Pressure Study of Perovskite-Like Organometal Halide: Band-Gap Narrowing and Structural Evolution of [NH-(CH)-NH]CuCl.

Searching for nontoxic and stable perovskite-like alternatives to lead-based halide perovskites for photovoltaic application is one urgent issue in photoelectricity science. Such exploration inevitably requires an effective method to accurately control both the crystalline and electronic structures. This work applies high pressure to narrow the band gap of perovskite-like organometal halide, [NH-(CH)-NH]CuCl (DABCuCl), through the crystalline-structure tuning.

Effect of pressure on heterocyclic compounds: pyrimidine and s-triazine.

We have examined the high-pressure behaviors of six-membered heterocyclic compounds of pyrimidine and s-triazine up to 26 and 26.5 GPa, respectively. Pyrimidine crystallizes in Pna2₁ symmetry (phase I) with the freezing pressure of 0.

Pressure-induced isosymmetric phase transition in sulfamic acid: a combined Raman and x-ray diffraction study.

High-pressure behaviors of hydrogen-bonded molecular crystal, sulfamic acid (NH3(+)SO3(-), SA), have been investigated using Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques up to the pressure of ~20 GPa. Under ambient conditions, molecules of SA are arranged in puckered layers and held together by hydrogen bonding and electrostatic interactions. It is proved by the Raman results that SA undergoes the molecular conformation changes in the pressure range 8.

Exploration of the pyrazinamide polymorphism at high pressure.

We report the high-pressure response of three forms (α, δ, and γ) of pyrazinamide (C(5)H(5)N(3)O, PZA) by in situ Raman spectroscopy and synchrotron X-ray diffraction techniques with a pressure of about 14 GPa. These different forms are characterized by various intermolecular bonding schemes. High-pressure experimental results show that the γ phase undergoes phase transition to the β phase at a pressure of about 4 GPa, whereas the other two forms retain their original structures at a high pressure.

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4●3H2O.

High-pressure Raman scattering and synchrotron X-ray diffraction measurements of sodium squarate (Na(2)C(4)O(4), SS) are performed in a diamond anvil cell. SS possesses a rare, but typical structure, which can show the effect of face-to-face π-stacking without interference of other interactions. At ~11 GPa, it undergoes a phase transition, identified as a symmetry transformation from P2(1)/c to P2(1).

Synthesis and high-pressure transformation of metastable wurtzite-structured CuGaS2 nanocrystals.

The metastable wurtzite nanocrystals of CuGaS(2) have been synthesized through a facile and effective one-pot solvothermal approach. Through the Rietveld refinement on experimental X-ray diffraction patterns, we have unambiguously determined the structural parameters and the disordered nature of this wurtzite phase. The metastability of wurtzite structure with respect to the stable chalcopyrite structure was testified by a precise theoretical total energy calculation.

Pressure-induced phase transition in N-H···O hydrogen-bonded molecular crystal oxamide.

The effect of high pressure on the structural stability of oxamide has been investigated in a diamond anvil cell by Raman spectroscopy up to ∼14.6 GPa and by angle-dispersive X-ray diffraction (ADXRD) up to ∼17.5 GPa.

Effect of high pressure on the typical supramolecular structure of guanidinium methanesulfonate.

We report the high-pressure response of guanidinium methanesulfonate (C(NH(2))(3)(+)·CH(3)SO(3)(-), GMS) using in situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques up to the pressures of ~11 GPa. GMS exhibits the representative supramolecular structure of two-dimensional (2D) hydrogen-bonded bilayered motifs under ambient conditions. On the basis of the experimental results, two phase transitions were identified at 0.

Pressure-induced phase transition in guanidinium perchlorate: a supramolecular structure directed by hydrogen bonding and electrostatic interactions.

In situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) experiments have been performed to investigate the response of guanidinium perchlorate (C(NH(2))(3)(+)·ClO(4)(-), GP) to high pressures of ∼11 GPa. GP exhibits a typical supramolecular structure of two-dimensional (2D) hydrogen-bonded ionic networks at ambient conditions. A subtle phase transition, accompanied by the symmetry transformation from R3m to C2, has been confirmed by obvious changes in both Raman and XRD patterns at 4.

Pressure-induced phase transitions in ammonium squarate: a supramolecular structure based on hydrogen-bonding and π-stacking interactions.

We report the results of high-pressure Raman and X-ray diffraction measurements performed on ammonium squarate ((NH(4))(2)C(4)O(4), AS), a representative supramolecular architecture based on hydrogen bonding and π-stacking interactions, at various pressures up to 19 GPa. Two phase transitions at ∼2.7 GPa and in the pressure range of 11.

Structural properties and halogen bonds of cyanuric chloride under high pressure.

The effects of high pressure on cyanuric chloride (C(3)N(3)Cl(3)), a remarkable crystal structure dominated by halogen bonds, have been studied by synchrotron X-ray diffraction and Raman spectroscopy in a diamond anvil cell. The results of high pressure experiments revealed that there was no obvious phase transition up to 30 GPa, indicating that halogen bonding is an effective noncovalent interaction to stabilize the crystal structure. Moreover, cyanuric chloride exhibited a high compressibility and a strong anisotropic compression, which can be explained by the layered crystal packing.

Pressure-induced phase transition in hydrogen-bonded supramolecular structure: guanidinium nitrate.

In situ Raman scattering and synchrotron X-ray diffraction have been used to investigate the effects of high pressure on the structural stability of guanidinium nitrate (C(NH(2))(3)(+).NO(3)(-), GN), a representative two-dimensional supramolecular architecture of hydrogen-bonded rosette network. This study has confirmed a structural phase transition observed by Raman scattering and X-ray diffraction at approximately 1 GPa and identified it as a space group change from C2 to P2(1).