High Pressure Study Of Large Fullerenes And Endohedral Metallofullerenes

Due to the unique structures and novel properties, fullerenes have attracted much attention in different fields, such as physical, materials and chemistry. Some new phenomena of fullerenes under high pressure have been observed, such as 1D, 2D,3D polymerization, even a non-traditional crystal structure: ordered amorphous carbon cluster(OACC) structure. These interesting structures have excellent mechanical and optical properties, even high hardness similar to diamond, which provide important ways to exploring new phenomenas, structures and properties.However, previous studies mainly focused on small fullerenes C60 and C70. Large fullerenes and endohedral metallofullerenes(EMFs) are important members of fullerenes family, and have attracted much attention. Unfortunately, due to the low yield, even the studies for basic structure and physical properties of large fullerenes and EMFs are lacking. No information exists on the corresponding high pressure study. For large fullerenes and EMFs, the basic structural information, the structural stability and deformation under high pressure, and whether they can form the interesting structures like C60 and C70 are basic topics worthing studying. Recently,the progresses in yield make such studies possible.Particularly, the interesting sturctures of C60 are closely relaed to the deformation of fullerene cage. But due to high molecular symmetry, the understanding for the deformation is still unclear. Compared with C60 and C70, large fullerenes and EMFs have a larger frame and lower symmetry, which may lead to a more obvious deformation and thus provide a good model to study the deformation of carbon cages.Based on these aspects, we carried out high pressure studies on large fullerene C96 and several EMFs, including Sm@C88,Sm@C94, Sm@C90 and solvated Sm@C90.The results of study are as follow:1. We have studied the structural stability and deformation of D3d-C96 under pressure up to 22 GPa by infrared spectroscopy. The infrared-active vibrational modes of D3d-C96 at ambient conditions have been assigned for the first time combined with theoretical calculation. The results of analyzing the infrared spectroscopy indicate an anisotropic deformation of the carbon cage upon compression. The deformation of C96 molecule starts from the parts linking tubular and bowl-shaped parts. The tubular deforms more obviously than the bowl-shaped parts, and collapses firstly. The carbon cage deforms from ellipsoidal to a peanut-like shape, similar to the deformation process of C90. The carbon cage of C96 collapses at19.5 GPa, and the collapse is reversible completely. This study provides a complete picture on structural stability and deformation process of nanotube-like large fullerenes at the atomic level. It helps us to understand the complex change in fullerenes/ signal-walled carbon canotubes.2. We have studied the structural stability and deformation of Sm@C88 and Sm@C94 under pressure by infrared spectroscopy combined with theoretical simulations. The infrared-active vibrational modes of Sm@C88 and Sm@C94 at ambient conditions have been assigned for the first time. The two different EMFs exhibit anisotropic deformation of the carbon cages upon compression. The parts of the carbon cage far away from Sm atom deform more obviously, suggesting that the trapped Sm atom plays a role in minimizing the compression of the adjacent bonds.The differentences are that the Sm@C88 cage changes from ellipsoidal to approximately spherical around 7 GPa. The carbon cage deforms significantly above7 GPa, from spherical to a peanut-like shape and collapses at 18 GPa. Pressure induced a significant reduction of the band gap of the crystal,resulting from that 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. The band gap of Sm@C94 decreases slowly below 8 GPa, and decreases obviously in the region of 8-14 GPa due to the obvious deformation and pressure-induced enhance of intermolecular interaction,then change slightly above 14 GPa resulting from that the pressure-induced enhanceof intermolecular repulsive force hinder the intermolecular approaching.We have studied the structural deformation of Sm@C88 by infrared spectroscopy in a low temperature range of 7.37 to 293 K. The results of analyzing the infrared spectroscopy indicate that the Sm@C88 cages have an orientational disorder-order transition at 200 K and deform obviously at 100 K. The parts of the carbon cage far away from Sm atom deform more obviously, suggesting an anisotropic deformation of the carbon cage under low temperature, which results from the low temperature-induced enhance of the interaction between Sm and the carbon cage.The interaction between Sm and the neighboring parts minimizes the change of the adjacent bonds. The band gap of the material decreases slightly with lowing temperature, indicating low temperature has a little influence on the electronic property of Sm@C88.Such studies give the basic structural information, stability and deformation of EMFs, and the effect of the interaction between the trapped metal atom and the carbon cage on the structural evolution of the hosting carbon cage and the electrical properties at the atomic level. Such studies help to improve our understanding of the structure and properties of EMFs and the unique metal-cage interaction. These provide a very useful reference for future research on the structures and properties of EMFs and the possibility to create novel, EMF-based functional materials.3. We have firstly synthesized solvated Sm@C90 microrods by a solution drop-drying method, and then studied the transformations under high pressure by in situ Raman and infrared spectroscopy and compared with pristine Sm@C90. We found that the pressure-induced structural evolutions of Sm@C90 in the two samples both undergo deformation and collapse. The band gap of both samples decrease with increasing pressure. The trapped Sm atom plays a role in restraining the compression of the adjacent bonds. The solvent play a role in protecting Sm@C90 against collapse in the region of 12-20 GPa, decreasing and postponing the change of band gap.Above 30 GPa, the carbon cages collapse. Released from 45 GPa, the collapsed Sm@C90 form a new ordered amorphous carbon cluster(OACC) structure containing metal atoms. This study gives give the basic structural information,stability and deformation of Sm@C90, and extends the OACC structure on EMFs and opens the door for the creation of new carbon materials with desirable structural and physical properties when suitable starting materials are selected.