The Structure Of Hydrogenated Fullerenes Under High Pressure And The Fullerenes Doped With Alkali Metals

Hydrogenated fullerenes have attracted much attention due to its potential application in the lithium ion cell and hydrogen storage materials. C60H36 and C₆₀H₁₈ are the most prominent representatives in this class of compounds, which are the most stable hydrogenated derivatives of the fullerene. As typical derivatives of the fullerenes, it is also interesting to explore high pressure induced phase transformation of hydrogenated fullerenes on the analogy of C60 case. In addition, due to potential applications in energy materials, it is very important to obtain the information about the structural and chemical stability of the hydrogenated fullerenes under high pressure. Meletov etal. and Kawasaki etal. have successfully studied the vibration and structure properties of C60H36 under high pressure. However there are some argues about the phase transformation.In this paper, we further study the structural properties and the stability of hydrogen in the fullerene molecular cage under high pressure. We employ high pressure in suit IR spectra with more advantages in avoiding interference from luminescence. In-house high pressure in suit IR spectra instrument is designed by PhD Liu zhenxian. In addition, C₆₀H₁₈ due to its single C3V isomer, which successful synthesized with high purity by Thomas W?gberg is selected. Finally high pressure in situ angle-dispersive synchrotron x-ray diffraction experiments are also applied and enough data points are acquired. High pressure infrared experiments and X-ray diffraction experiments have been applied for C₆₀H₁₈ up to 32 GPa and 10.2 GPa, respectively.We analyze the diffraction data and obtain the cell parameters of phase with Reitveld refinement, the pattern is assigned to a fcc structure with lattice constants of a=14.56?, The sample is stable when the pressure is up to 32GPa and no phase transition has been observed. we fit the volume-pressure experimental data for the fcc structure using the Murnaghan equation, we obtain the bulk modulus B0 = 21±1.16GPa (B0`=6.68±0.25GPa), which is higher than pristine C60. In high pressure IR spectra, we find the peak frequencies in high frequency region attributed to the C-H symmetric and asymmetric stretching vibration modes; and these vibration frequencies decrease with increasing pressure. This frequency decrease may be due to intermolecular hydrogen bonds strengthen with pressure as the intermolecular distances decrease, even the C-H-C vibration modes forming in high pressure. The strengthening of intermolecular hydrogen bonds protects the structure from distortion. The hydrogen may play an important role in the stability of the materials. In particular it may prevent the pressure-induced polymerization that is typical of pristine C60 under high-pressure and high temperature treatment. The incorporation of hydrogen affects the pressure-induced phase transition of the rotational disorder–order nature analogously to the case of pristine C60. This may be the main reason for the higher bulk modulus of C₆₀H₁₈ compared with C60 powders. We also give a speculation about the changing behavior of C-H vibration group in fullerene molecular cage under high pressure.In this paper, we also study the synthesize methods of alkali-metal-doped C60 nanowires, which doped with Na. The thermal diffusion method is employed. Different conditions such as temperature, time, and atmosphere pressure are systemically studied. The result from the samples of the Raman spectra indicates that it is Na4C60. However the amount of the samples is too little to further study its properties. There are still lots of works to do.