A molecular dynamics study of impurity desorption from solid clusters of rigid C60 molecules

Abstract

We investigate through molecular dynamics ͑MD͒ simulation the desorption at high temperature of Kr atoms from solidlike clusters of rigid C 60 molecules. The inert gas particles are initially allocated in the interstices of a solid C 60 matrix, placed at the center of the simulation box with empty space around; desorption is then monitored as a function of the average temperature achieved at the end of different MD run. The assumed sphericalized two-body potential practically excludes endohedral absorption of Kr inside the fullerene cage and is potentially suitable to model impurity species other than the one here considered. The obtained results indicate that in the range of temperatures 1200рTр1500 K the solid matrix of C 60 particles is stable, and that only a part of the 'doping' Kr atoms is able to escape from the C 60 'environment', the rest remaining trapped inside the fullerene cluster in a configuration in which the rare gas atoms occupy on the average the octahedral sites of the host matrix. The implications of such results as far as the role of impurity species in determining the experimentally observed high temperature instability of fullerites accompanied by carbon amorphization, are discussed.

Phase and Glass Transitions in Short-Range Central Potential Model Systems: The Case of C60

“…The paper focuses in particular on the Girifalco potential for fullerene C 60 . This model can be considered as “marginally” short-range in the sense that, whereas in colloidal and protein systems the interaction between (model) macroparticles reduces practically to zero within a fraction of the particle diameter and the liquid−vapor equilibrium is only metastable, in the Girifalco model the decay length of interactions is slightly greater than the fullerene diameter and a stable liquid phase does exist, albeit confined to a temperature interval smaller than 100 K, ,− with no experimental evidence of it hitherto reported. − Such characteristics appear consistent with early speculations about the “elusive diffusive” nature of liquid C 60 , as well as with recent evidences of the absence, in this peculiar fluid, of cage effects in the velocity autocorrelation functions, and of collective phenomena, ordinarily observed in simple liquids …”

High-Temperature Glass Transition in Model C60

“…1,2 Another glassy phase, associated with positional disorder of C 60 , might also be formed upon quenching from the (normal or supercooled) liquid phase of this fullerene. Liquid C 60 , however, has not yet been observed, [3][4][5][6][7] although its existence has been predicted [8][9][10][11][12][13][14] for a spherically symmetric pair potential model of C 60 due to Girifalco. 15 The temperature range of the liquid pocket is rather narrow, the triple and critical point temperature being T tr = 1880 K and T cr = 1940 K, respectively; 13,14 the liquid is thus "nearly critical" in any case.…”

Glass transition in fullerenes: Mode-coupling theory predictions

“…[8,9,10,11]). This instability could be due to impurities [12], or be a collective effect involving interfullerene interactions [9].…”