CORRELATION OF LOW-TEMPERATURE MICROPLASTICITY ANOMALIES WITH STRUCTURE TRANSFORMATIONS IN C-60 CRYSTALS

Abstract

Structure, microhardness and slip systems were studied on C-60 crystals of high purity in the temperature range 30-290 K, which includes the fcc --> sc phase transition at T-c = 260 K and the orientational glass region T < 100 K. A step-like change of both the lattice parameter and the microhardness was recorded when passing through T-c, as well as the formation of slip lines near the indentations in both phases. The slip system <110>{111}, operative at room temperature in the FEC phase, is shown to retain its activity below T-c, in the sc phase. In the region where the orientation 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 chancier ol the dislocation motion in C-60 crystals, which make it possible to explain the microplasticity anomalies observed.