C60高压X射线衍射研究

 采用同步辐射X光源和能量色散法对高纯C₆₀粉末样品进行高压原位X光衍射实验。由金刚石对顶压砧高压装置（DAC）产生高压,用已知状态方程的Pt粉末作内标,由Pt的衍射数据确定样品压力,最高压力达30 GPa。实验结果表明：室温常压下原始C₆₀样品为面心立方结构,晶格常数a=1.420 86 nm。高压下C₆₀的结构有所变化：从p=13.7 GPa开始,(311)线发生劈裂,形成低对称相;随着压力增加,衍射线逐渐变宽,强度逐渐变弱,压力超过25 GPa,衍射背底隆起,C₆₀开始转化成非晶相;在30 GPa左右,衍射线条完全消失,标志着向非晶相转化过程的完成。人们也对C₆₀样品不同压力的高压“淬火”相进行了X光衍射实验。采用非静水压的装样方式,最高压力达44 GPa,结果在30 GPa以上,C₆₀也转变为非晶相。最后我们对C₆₀晶体的压致非晶化现象进行了初步的讨论。

X-RAY DIFFRACTION STUDIES ON C_(60) UNDER HIGH PRESSURE

In situ high pressure X-ray diffraction experiments have been done for super-pure C60 powder sample using synchrotron radiaton X-ray source and an energy dispersion detector. The pressure is generated by DAC. Pt was used as an inner pressure standard, whose EOS is known. The pressure of the sample was determined by the diffraction data of Pt. The maximum experimental pressure is 30GPa. The results indicate that crystal C60 has a fcc structure with lattice parameter a= 1. 42086nm at ambient condition; and the crystal structure of C60 was changed under high pressure. A lower symmetry phase reached at 13. 7GPa, marked by the splitting of diffraction line (311). Following the pressure increasing further, the diffraction lines were broaden continuously and their intensities became very week. The background raised obviously at about 25GPa, it showed that C60 crystal began to transform to an amorphous state. The diffraction lines disappeared wholly, thus the transformation to amorphous state was finished completely at about 30GPa.We also carried out X-ray diffractional experiments for C60 samples "quenched" at various pressures up to 44GPa. The samples were in nonhydrastatic pressures. The spectra showed that crystal C60 transformed to amorphous state beyond 30GPa.Finally, the phenomena of pressure-induced transition from crystal to amorphous state are discussed.