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.
- 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.
- The structure and the dynamics of solid C60 are important for
understanding its other properties.
- The basic results: There are two different phases of C60 with the
transition temperature about 255 K. The transition is a first-order one.
- The structure of C60 at room temperature is fcc, in which the
molecules exhibit dynamic orientational disorder.
- 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.
- The low-temperature phase is an orientationally ordered sc
- Calorimetry measurements confirm that the transition is first-order.
- Below the transition the molecules jump between
- The behavior at the phase transition is strongly influenced by trace
impurities and solvent.
- The transition has been probed by dynamical techniques
(NMR, Raman scattering).
- Increasing pressure both increase the transition temperature and
reduces orientational fluctuations of the C60 molecules in the
- The Young's modulus has an 8% jump at the transition.
- There is a similar phase transition in solid C70 with a
hysteresis in the transition temperature.
- This paragraph summarizes the main points of the paper.
- "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
- "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).
- "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).
- "Structure, dynamics and ordering transition of solid C60,"
P. A. Heiney, J. Phys. Chem. Solids 53, 1333 (1992).
- "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).
Your comments and
suggestions are appreciated.
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