Tang Tong B.1, Gu Min1,2
1Department of Physics, Hong Kong Baptist University, Kowloon, Hong Kong SAR, P.R. China
2National Laboratory of Solid State Microstructures, Nanjing University, Nanjing, P.R. China
Выставление онлайн: 19 марта 2002 г.
C60 pellets, charged respectively with He, Ne, Ar, and O2 under high pressure, have been studied with complex impedance spectroscopy. The latter two were found to depress the temperatures for both phase change (Tc) and glass transition (Tg), although in time shifts stayed almost constant in the Ar, but decreased in the O2, case. The effective barriers for the glass transition were determined as 218±15 in Ar0.49C60, and 182±20 meV in(O2)0.5C60. In contrast, neither He nor Ne had discernible influence on these materials parameters. These observations could be explained as follows. (1) Interstitial Ar causes a reduction in energy barrier and a weakening in the restorative force of the cage libration mode, thereby depressing Tc. (2) For (O2)0.5C60, a coupling between the cage libration and the tumbling of an O2 di-atomic molecule further weakens the restorative force, so that a larger temperature shift results. (3) Its tumbling motion makes O2 more susceptible to the "paddle wheel" action of rotating C60, and more easy to diffuse even under ambient conditions. TBT was suported by The Hogn Kong Baptist University under FRG/97-98/II-70; GM, by a Croucher Fellowship at HKBU and in Nanjing by the NSF of China under Grant N 10074031.
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