Effects of pressure and ambient species on orientational ordering in solid C{sub 70}

Journal Article · Fri Mar 01 04:00:00 EST 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.53.5211· OSTI ID:279083

Samara, G A; Hansen, L V; Morosin, B; Schirber, J E ^[1]

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1. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

The effects of hydrostatic pressure on the orientational ordering phase transitions in solid C{sub 70} were investigated by differential thermal analysis (DTA) using helium and nitrogen gases as pressure-transmitting media. The different observed responses in these media for the different transitions and for different samples, as well as some irreversible pressure/temperature cycling effects, have provided much insight into the ordering processes and into the influence of interstitial lattice impurities on these processes. Compression of the lattice strongly hinders the rotational motion of the C{sub 70} molecules, especially their high-temperature tumbling motions, and results in stabilization of the ordered low-temperature phases. This feature reflects the weak van der Waals intermolecular bonding and the high sensitivity of the rotational barriers to intermolecular separation. In microscopic terms, the results can be understood in terms of pressure-induced enhancement of the nesting of electron-rich and electron-poor regions of the C{sub 70} molecular cages. Observations of the evolution of DTA spectra during compression and as a function of time after release of pressure revealed a variety of nearly degenerate (in energy) configurations which are believed to be due to either hindered rotations of the molecules by interstitial impurities or to different stacking sequences of the monomolecular C{sub 70} layers. The results are compared with earlier findings on solid C{sub 60}. {copyright} {ital 1996 The American Physical Society.}

• Research Organization: Sandia National Laboratory
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 279083
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 9 Vol. 53; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DIFFERENTIAL THERMAL ANALYSIS
FULLERENES
IRREVERSIBLE PROCESSES
ORDER PARAMETERS
PHASE TRANSFORMATIONS
PRESSURE DEPENDENCE
ROTATIONAL STATES
STRUCTURAL MODELS