Correlation of low-temperature microplasticity anomalies with structure transformations in C60 crystals

Abstract

Structure, microhardness and slip systems were studied in C60 crystals of high purity in the temperature range 30−290 K, which includes the fcc→sc phase transition at Tc = 260 K and the orientational glass region T < 100 K. A step-like change of both the lattice parameter and the microhardness when passing through Tc have been recorded, as well as the formation of slip tracks near the indentations in both phases. The slip system ⟨110⟩{111}, operative at room temperature in the fcc phase, is shown to retain its activity below Tc, in the sc phase. In the region where the orientational glass is formed, we have found a kink-like anomaly on the microhardness vs temperature curve; this anomaly correlates with a weak anomaly in the temperature dependence of the lattice parameter. Assumptions are formulated concerning the character of the dislocation motion in C60 crystals, which make it possible to explain the microplasticity anomalies observed.