MODIFICATION OF THE LOW AND HIGH-TEMPERATURE METAL-SEMICONDUCTOR TRANSITIONS IN (V1-XCRX)(2)O-3 CERAMICS BY HIGH-ENERGY HEAVY-ION IRRADIATION

Chromium doped vanadium sesquioxide [(V1-xCrx)(2)O-3] ceramic samples have been irradiated using high energy lead ions (Pb-208 : 6.032 GeV) and medium energy chromium ions (Cr-52 : 572Mev) at various fluences ( 4 x 10(11) to 1.1 x 10(14) ions/cm(2)) and doping rates (x = 0.3% and 0.6%). The effects of the irradiation temperature (77K and 300K) on th e modification of the electrical and structural properties of irradiat ed ceramics (V1-xCrx)(2)O-3 (x = 0.003 and 0.007) have been studied us ing resistivity measurements as a function of temperature, XRD and TEM analysis. The structural analysis has shown the existence of disconti nuous latent tracks in which the damaged volume fraction is concentrat ed, Because of internal stress around these tracks, lead ions irradiat ion induced temperature shifts and broadenings of the LT and HT transi tions. The stabilization of a grain fraction in the metallic state ind uces a reduction of the PTC-like effect (HT transition), Irradiations by chromium ions create bilayered samples as the ion mean projected ra nges were smaller than the sample thickness. The bilayered structure i s characterized by two transitions at low temperature. Concerning the high temperature PTC-like transition, the NTC behavior after this tran sition, which is a general limitation to the use of the PTC device, ha s been considerably attenuated by the bilayered structure.