Electron radiation damage in H.C.P. metals—II. The nature of the defect clusters in Zn and Cd formed by irradiation in the HVEM

Positron lifetime calculations for defects in Zn

“…There are several possible configurations that can give rise to interstitial-type loops in hcp crystals, but we have selected only those that are the most favoured in the potential model used. The planar clusters formed by O-type interstitials (the notation for the selfinterstitial sites is that currently used and introduced by Johnson and Beeler [11]) result in the most stable configurations among all the possible ones that can be generated by considering all the favourable cases [9]; it has been found that these planar agglomerates generate faulted interstitial-type loops with b = (1/2) 0001 , in agreement with transmission electron microscope observations [10]. Unrelaxed configurations formed by two adjacent layers of interstitials can relax to double loops.…”

“…It demonstrates a strong anisotropy of vacancy migration, with preferential jumping on the basal plane, in agreement with the experiment and gives an improved value for the stacking fault energy in comparison with previous potentials. Moreover, the properties of single interstitials and interstitial clusters derived from the model explain satisfactorily some experimental observations concerning the formation of interstitialtype dislocation loops [10]. Details on the potential development and defect properties are given elsewhere [8,9].…”

“…The 1 100 -type projections of the two structures are shown in figures 3(a) and 3(b). It is recalled that faulted and unfaulted double loops have been observed by transmission electron microscopy in electron-irradiated Zn [10].…”

On the origin and behavior of irradiation-induced c-component dislocation loops in magnesium

“…The I1-I2 type loops can further lower the energy from an unfaulted process via a dislocation reaction with a Shockley partial loop shear on the stacking fault plane as: [31,44]. This bridges the conventional understanding of I1-N type of double-layer loop formation in hcp Zn [44] and Zr [31].…”

“…The stationary nature of c-component dislocation loops on the basal plane can promote more complicated multiple-layer loop structure formation. Double-layer loop structure is commonly observed in all hcp metals under irradiation, including Zr, Zn, Cd and Mg [5,11,17,21,28,31,36]. In quenched Mg, double-or even quadruple-layer vacancy c-component dislocation loops were reported [37,38].…”