C-60 with pentagon orientational ordering: a dielectric study on fulleritecharged with CO

In solid C-60, Complex impedance spectroscopy measurements revealed a relax ational process due to glass transition. However, the spectral features ass ociated with this relaxation became indiscernible, when CO molecules are pr esent at octahedral sites in molar ratio exceeding 0.67. We explain this ph enomenon by the existence of a phase with almost purely pentagon oriented C -60, and this phase is favored by a negative chemical pressure on C-60 latt ice exerted by CO, as well as the electrostatic interaction between the two . (C) 2001 Elsevier Science B.V. All rights reserved.