THERMAL-EXPANSION MEASUREMENTS OF C-60 C-70 MIXED-CRYSTALS/

The results of thermal expansion and room temperature powder X-ray dif fraction measurements on (C-60)(1-x)(C-70)(x) fullerene alloys are pre sented. Samples have been prepared by controlled condensation from the vapor phase. Strong anomalies in thermal expansion occur at the fee t o sc phase transition in C-60-rich, and hcp to distorted hcp one in C- 70-rich crystals, respectively. The phase transition temperature dimin ishes with rising mixture ratio both on the C-60-rich (similar to -4K/ 1%, C-70) and on the C-70-rich (similar to -20K/1% C-60) side of the p hase diagram. This suggests the existence of an orientational glass ph ase on the C-70-rich side of the phase diagram (in agreement with ther mal expansion measurements on sample with 70%, C-70, which show no sig n of the phase transitions at temperatures above 80 K). (C) 1997 Elsev ier Science Ltd.