“…Depending on the treatment of the sample, also a hexagonal closepacked structure exists. 1,2,6,7 Upon cooling from the fcc phase, a transition to a rhombohedral phase ͑space group R3m) occurs, followed by a transition to a monoclinic phase around 295 K. [2][3][4] Unlike in solid C 60 where the transition from the Fm3m to the Pa3m phase is essentially a phenomenon of orientational ordering, [8][9][10] while the centers of mass of the molecules still occupy an fcc lattice, the transition from the cubic to the rhombohedral phase in solid C 70 is due to a coupling of orientational quadrupoles of T 2g symmetry to trigonal shear strains. 11,12 Such a bilinear coupling which is characteristic for ferroelastic transitions, 13 is favored by the elongated shape of the C 70 molecule.…”