Number 91 (Story #3), August 12, 1992 by Phillip F. Schewe and Ben Stein|
BUCKYBALL CRYSTALS HAVE DIELECTRIC PROPERTIES that require the existence of a permanent, non-symmetrical distribution of electric charge in the material at lower temperatures. Below 260 K, C-60 crystals undergo a phase change in which the lattice structure changes and the individual molecules assume a fixed orientation instead of rotating freely in the lattice. Theorists previously believed that the molecules in the low temperature phase were oriented in such a way as to ensure a zero electric dipole. However, Glenn B. Alers and Brage Golding (517-355-9708) of Michigan State University and their co-workers at AT&T Bell Labs found that single C-60 crystals subjected to low-frequency electric fields exhibited a dielectric response containing frequency-dependent contributions that require the existence of permanent dipoles in the material. The researchers propose that the dipoles are induced by misoriented C-60 molecules which maintain their own spherical symmetries but break the charge symmetry of the lattice. These imperfections in the C-60 lattice would have implications for the optical and nonlinear properties of buckyball films, and may mean that the crystal can interact with a wider variety of electromagnetic frequencies than previously thought. (Science, 24 July 1992).