Sample Student Sentence Outline

Orientational Ordering and Orientational Transition in C60 Crystals

Abstract: Solid C60 forms a fcc structure at room temperature, in which the molecules exhibit orientational disorder. At 255 K the molecules develop orientational order via a first order phase transition to a sc lattice. Below the transition the molecules jump between symmetry-equivalent orientations. The transition temperature increases with pressure. Similar effects are seen in C70.

1. The identification of the molecular structure of C60 and its subsequent synthesis and separation in solid form have generated interest in this form of carbon which possesses many exciting properties.
2. The structure and the dynamics of solid C60 are important for understanding its other properties.
3. The basic results: There are two different phases of C60 with the transition temperature about 255 K. The transition is a first-order one.
4. The structure of C60 at room temperature is fcc, in which the molecules exhibit dynamic orientational disorder.
5. X-ray diffraction measurements reveal a phase transition from the fcc phase to a low-temperature phase. In the transition there is a jump in lattice parameter jump.
6. The low-temperature phase is an orientationally ordered sc structure (Pa3).
7. Calorimetry measurements confirm that the transition is first-order.
8. Below the transition the molecules jump between symmetry-equivalent orientations.
9. The behavior at the phase transition is strongly influenced by trace impurities and solvent.
10. The transition has been probed by dynamical techniques (NMR, Raman scattering).
11. Increasing pressure both increase the transition temperature and reduces orientational fluctuations of the C60 molecules in the low-temperature phase.
12. The Young's modulus has an 8% jump at the transition.
13. There is a similar phase transition in solid C70 with a hysteresis in the transition temperature.
14. This paragraph summarizes the main points of the paper.

Some references

1. "Orientational Ordering Transition in Solid C60," P. A. Heiney, J. E. Fischer, A. R. McGhie, W. J. Romanow, A. M. Denenstein, J. P. McCauley, Jr., and A. B. Smith III, Phys. Rev. Lett. 66, 2911 (1991).
2. "Discontinuous volume change at the orientational-ordering transition in solid C60," P. A. Heiney, G. B. M. Vaughan, J. E. Fischer, N. Coustel, D. E. Cox, J. R. D. Copley, D. A. Neumann, W. A. Kamitakahara, K. M. Creegan, D. M. Cox, J. P. McCauley, Jr., and A. B. Smith III, Phys. Rev. B 45, 4544 (1992).
3. "Crystal structure and bonding of ordered C60," W. I. F. David, R. M. Ibberson, J. C. Matthewman, K. Prassides, T. J. S. Dennis, J. P. Hare, H. W. Kroto, R. Taylor, and D. R. M. Walton, Nature 353, 147 (1991).
4. "Structure, dynamics and ordering transition of solid C60," P. A. Heiney, J. Phys. Chem. Solids 53, 1333 (1992).
5. "Pressure Dependence of the Orientational Ordering in Solid C60," G. A. Samara, J. E. Schirber, B. Morosin, L. V. Hansen, D. Loy, and A. P. Sylwester, Phys. Rev. Lett. 67, 3136 (1991).