Observation of ultrasound velocity gradient in fullerene ceramics by acoustic microscopy

A scanning acoustic microscope is used to study the distribution of elastic properties in small samples (diameter 3 x 2 mm(3)) of new hard phases of C -60 The specimens under investigation were synthesized from pure C-60 powde r under pressure P = 8 GPa in the temperature range 500-1650 K. The time-of -flight mode was used for bulk sound wave velocity determination in a direc tion parallel to the cylinder's axis. Longitudinal sound wave velocities gr eater than 10 000 m/s were found for all specimens treated at temperatures higher than 1000 K. Using the B-scan mode allowed us to observe the velocit y gradient in the sample's periphery. The heterogeneous internal structure of the specimen is visualized in the images formed in C- and B-scan modes. (C) 2000 Elsevier Science B.V. All rights reserved.