A strategy for preparing hybrid carbon structures with amorphous carbon clusters as hard building blocks by compressing a series of predesigned two-component fullerides is presented. In such constructed structures the building blocks and their boundaries can be tuned by changing the starting components, providing a way for the creation of new hard/superhard materials with desirable properties.

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A schematic diagram of the UC luminescence modulation mechanism.

Tuning the intertube interaction and the topological structure of carbon nanotubes by the application of pressure may obviously affect their properties such as optical and electronic properties. However, characterizing such changes is still challenging. Here, we performed polarized Raman scattering studies on aligned multiwalled carbon nanotube arrays (MWNTAs). Unlike researchers from the previous literature, we found that the MWNTAs exhibit a polarization dependence similar to that of isolated single-walled carbon nanotubes at ambient conditions. Upon compression, the polarization dependence weakens gradually with increasing pressure up to ∼20 GPa, which has been discussed in terms of pressure-induced enhancement of intertube interactions. At around 20 GPa, the depolarization effect vanishes, which can be explained by the formation of interlinked sp3 bonding in the MWNTAs. Our results show that polarized Raman spectroscopy is an efficient method to explore not only intertube interaction but also structural transition changes in MWNTs, which overcome the difficulty that MWNTs have no obvious fingerprints like those of single-walled carbon nanotubes in the study of structural transformations.

Polynitrogen compounds have attracted great interest due to their potential application in the field of high-energy-density materials (HEDMs). Alkali azides are powerful candidates for the high-pressure preparation of HEDMs. In this work, we report a study of the crystal structure evolution and chemical transformation of NaN 3 under high pressure by in situ Raman spectroscopy and synchrotron X-ray diffraction methods up to 57.9 GPa. The initial rhombohedral NaN 3 transforms into the monoclinic C2/m-NaN 3 at 0.6 GPa, which is in agreement with previous studies. The monoclinic NaN 3 transforms into the tetragonal I4/mcm-NaN 3 at 15.5 GPa. With further compression, in the pressure range of 19.6−21.7 GPa, both the Raman spectrum and X-ray powder diffraction (XRD) diffraction pattern indicate the chemical transition from NaN 3 to new kinds of Na−N compounds with the appearance of experimental signals, which cannot be attributed to NaN 3 . It is very likely that a partial chemical transformation from NaN 3 to NaN 5 occurs at 19.6 GPa. NaN 5 is not stable at ambient conditions upon decompression. Our study indicates that NaN 5 can be formed by cold compression of NaN 3 , providing a potential route for the synthesis of binary alkali pentazolate compounds.