Phase diagram of the C[sub 60]/C[sub 70] system

Evolution of molecular ordering and phase transitions in C60/C70solid solutions

“…For x in the 0.15 ≤ x ≤ 0.68 range, the anomalies in the c P curves are clearly absent indicating that the samples do not suffer any phase transition down to 5 K. The absence of possible imperceptible weak and smeared out anomalies in the c P curves for these concentrations was checked by plotting the data (not shown) in ways that otherwise would accentuate their presence (for example c P /T vs. T or c P /T vs. T 2 ). In the remaining 0 ≤ x ≤ 0.014 range, anomalies in c P show up again, at temperatures that increase with decreasing x terminating for pure C 70 at x = 0 in an anomaly that takes place around 285 K. For this range, thermal hysteresis associated with the anomalies is of no more than 2 K. A proposed (x, T) phase diagram for (C 60 ) x :(C 70 ) 1-x constructed from data reported by McGhie et al [13] and Havlik et al [6,22,23] is depicted in Fig. 4a.…”

“…Some authors report complete C 60 /C 70 miscibility for crystals grown from the vapour phase but a large miscibility gap is detected in the middle range of the mixed system if crystals are grown from solution [20]. Other authors, however, conclude that a miscibility gap exists even for samples grown from vapour [21][22][23]. Like in pure C 60 , the high temperature phases of C 60 -rich solid solutions is cubic (fcc).…”

“…The twofold structural stability of pure C 70 is inherited to C 70 -rich solid solutions as some authors report samples for which the majority phase is either cubic [13] or hexagonal [6,22]. Even though a complete and unambiguous structural characterization of C 60 /C 70 solid solutions is still lacking, an approximate phase diagram has already been proposed [22,23]. From the theoretical side, some few efforts have been done to specifically treat C 60 /C 70 solid solutions.…”