INFLUENCE OF HIGH-ENERGY LEAD IRRADIATION ON THE LOW AND HIGH-TEMPERATURE METAL-SEMICONDUCTOR TRANSITIONS IN (V1-XCRX)(2)O-3 CERAMICS

Ceramic samples of chromium doped vanadium sesquioxide [(V1-xCrx)(2)O- 3] have been irradiated using high energy lead ions (208Pb:6.032 GeV) with various fluences (4 to 50 x 10(11) ions/cm(2)). Irradiations have been carried out under vacuum and at different temperatures. Irradiat ed samples have been characterized by electrical resistivity measureme nts as a function of temperature for low and high temperature transiti ons in the (V1-xCrx)(2)O-3 system. As the low and high temperature (LT and HT) phase transitions in this system correspond to different enth alpy variations, both transitions do not exhibit the same sensitivity to irradiation with heavy ions. Because of internal stress formation, lead ions irradiation induced shifts of the HT and LT transition tempe ratures and broadening of these transitions. Besides, stabilization of a fraction of the microcrystals in the sample in the metallic state l ed to the reduction of the PTC (Positive Temperature Coefficient)-like effect. The effects of the doping amounts (x = 0.003 and 0.007) and t he irradiation temperature (77 K and 300 K) on the modification of ele ctrical properties of the irradiated materials have been studied using resistivity measurements. Irradiations with a smaller doping rate and at 77 K lead to more significant changes in the thermal variations of the electrical resistivity. Large differences in electrical character istics have been observed between samples irradiated either in the met allic (300 K) or the semiconducting state (77 K) which showed that the sensitivity of (V1-xCrx)(2)O-3 ceramics to heavy ion irradiation is d ependent on the phase state and on its physical properties.