Dislocation loops resulting from vacancy and interstitial condensations are created from clusters of the respective defects, and either shrink or grow depending on the flux of defects reaching the embryo. Once they have reached a critical size, the loops become stable and grow until they unfault by interaction with other loops or with the network dislocations. Russell and Powell (1973) [5] have determined that interstitial loops nucleate much easier than vacancy loops because interstitial loop nucleation is less sensitive to vacancy involvement than is vacancy loop nucleation to interstitial involvement. The nucleation of loops is essentially a clustering pro­cess in which enough of one type of defect needs to cluster, in the presence of other types of defects, to result in a critical size embryo that will survive and grow.

The effects of irradiation temperature on the faulted Frank loop size and density in irradiated cubic silicon carbide (SiC) are shown in Figure 6.12(a) and (b), respec­tively. As the loops grew in size, their number density decreased. Figure 6.13 shows the effect of radiation dose (in dpa) on the faulted Frank loops in ion-irradiated cubic SiC at an irradiation temperature of 1400 °C.