Structural transformation in fullerene solids C-60 and C-70 at low temperatures - new insights

This paper reviews several recent investigations by the authors' group conc erning the structural transitions at low temperatures in the fullerene soli ds C-60 and C-70 In the case of C-60 it has been shown that the heat capaci ty variation with temperature in the ordered phase reflects the contributio n due to configurational reorientation of the molecules in the solid betwee n two energetically favourable orientations. Evidence is presented for the possible occurrence of an intermediate phase in solid C-60 in a narrow temp erature range just below the ordering transition. In the case of C-60 the n ature of transition as well as resulting low-temperature structure is kinet ic dependent. The equilibrium structure is obtained by the simultaneous fre ezing of all orientations of the molecules which brings to the fore the imp ortance of polar cap interaction between the molecules of the basal plane a nd those in the midplane. It has been shown by a potential energy calculati on that the structure obtained by slow cooling in experiment corresponds to the minimum energy configuration. (C) 2000 Elsevier Science Ltd. All right s reserved.