Temperature and photopolymerization effects in microhardness of C70 crystals

Abstract

The microhardness of C70 crystals was investigated in the temperature range of 295–425 K. The hardness gradually decreased with increasing temperature. The photoinduced hardening was observed after the long-time illumination of light. The hardening reached the maximum near the phase transition temperature of 348 K. These results are discussed and compared with those of C60 crystals.

Micromechanical properties of C70 single crystals in the temperature range 77–350 K

“…Return to the c 00 -phase occurred with overcooling by about 40 K at T 2 ¼ T c 0 -c 00 % 308 K, as in Ref. 12.…”

“…The lower boundary temperature is due to the method for obtaining low temperatures in the measuring device, 15 and the upper boundary is near the phase transition temperature for DHCP ! HCP: T c 00 -c 0 ¼ 348 K. 12 Microhardness measurements were performed at loads that met the condition that H V (P) % const: at T 300 K this was the minimum possible load P ¼ 0.05 N (indenter weight), and at T > 300 K the load was 0.02 N. lower than those obtained for cubic surface of C 60 crystals; they are presented for comparison in Fig. 8; at room temperature H V % 170 MPa in C 60 fullerite.…”

“…DHCP (c 0 -c 00 ), i.e., T c 0 -c 00 ¼ 305 K (Ref. 11) and a similar value T c 0 -c 00 ¼ 308 K. 12 A critical review of the data regarding the structure and phase transitions in C 70 fullerite is given in publication. 13 The structure of C 70 fullerite and its variations with temperature affect the physical as well as mechanical properties of the crystals.…”