A calorimetric study of phase transitions in C70 fullerene

✍ Scribed by Juliusz Swarakowski; Krystyna Palewska; Marcel Bertault

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 569 KB
• Volume: 220
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(94)00160-x

✦ Synopsis

Results of calorimetric studies of C,,, fullerene are reported. A phase transition at 195 K was found in pristine CT0 samples crystallized from toluene-containiag solutions, the material being identified as a 1: 1 C,,,-toluene adduct. Heating pristine samples over 430 K results in an irreversible decomposition of the adduct. Measurements of the specific. heat of thermally treated C,,, samples allow for identification of three phase transitions between 274 and 337 K: in addition to transitions at 274 and 337 K described in the literature, we found a transition at 307 K. The order-disorder transition at 274 K is associated with rotation of C,,, molecules around their long axes and is characterized by an insignificant hysteresis between heating and cooling runs. We determined the transition entropy to amount approximately to R In 4. The other transitions occurring at 307 and 337 K and exhibiting important hystereses are probably due to release of remaining rotational freedom associated with a re-arrangement of the crystal lattice between hexagonal and regular packings.