Abstract
We have studied the structural transformation of Sm@C88 under pressure up to 18 GPa by infrared spectroscopy combined with theoretical simulations. The infrared-active vibrational modes of Sm@C88 at ambient conditions have been assigned for the first time. Pressure-induced blue and red shifts of the corresponding vibrational modes indicate an anisotropic deformation of the carbon cage upon compression. We propose that the carbon cage changes from ellipsoidal to approximately spherical around 7 GPa. A smaller deformation of the carbon bonds in the area close to the Sm atom in the cage suggests that the trapped Sm atom plays a role in minimizing the compression of the adjacent bonds. Pressure induced a significant reduction of the band gap of the crystal. The HOMO-LUMO gap of the Sm@C88 molecule decreases remarkably at 7 GPa as the carbon cage is deformed. Also, compression enhances intermolecular interactions and causes a widening of the energy bands. Both effects decrease the band gap of the sample. The carbon cage deforms significantly above 7 GPa, from spherical to a peanut-like shape and collapses at 18 GPa.
Highlights
Deforms and forms links to nearest neighbors by [2 + 2 ] cycloaddition to form a 3D polymer at 15 GPa and 600 °C18
How Endohedral metallofullerenes (EMFs) deform under high pressure is still unknown and no information exists on how the confined metal atom affects the structural deformation of the carbon cage
We have studied the structural stability and deformation of Sm@C88 under pressure up to 18 GPa by IR spectroscopy combined with theoretical simulations
Summary
Deforms and forms links to nearest neighbors by [2 + 2 ] cycloaddition to form a 3D polymer at 15 GPa and 600 °C18. When solvated fullerene (C60*m-xylene) is compressed up to 60 GPa, the C60 cages collapse while the material still preserves a long-range ordered structure, containing amorphous carbon clusters as its basic units This material is ultra-incompressible and hard enough to indent diamond[20,21]. High pressure may tune the metal-cage interaction and make it possible to study the effects of the metal atom on the molecular deformation to improve our understanding of the unique metal-cage interaction. This may bring a new insight into the structural stability and the deformation process of fullerenes at the atomic level, making the prediction of new carbon phases possible. It has been found that the trapped metal atom supports the carbon cage against collapse under high pressure
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