New mechanism for radiation defect production and aggregation in crystalline ceramics

Nucleation and growth of sodium colloids in NaCl under irradiation: theory and experiment

“…The colloid growth rate is determined by the difference between the bias-induced absorption [4] and the exciton-induced emission [8] of F centers:…”

“…In 1977, Jain and Lidiard [3] have formulated a model, according to which, the dislocation bias for H centers was the driving force for the colloid growth in alkali halides in the same way as it is for void growth in metals under irradiation. The mechanism of dislocation climb [2] used in the Jain and Lidiard model, requires two H centers meeting each other at the dislocation core, and subsequently, the model was modified by Dubinko et al [4], who suggested that a dislocation can climb due to the production of a V F center (self-* Corresponding author: e-mail: h.w.den.hartog@phys.rug.nl, Phone: +3150-363-4789, Fax: +3150-363-4879 trapped hole neighboring a cation vacancy) induced by interactions between a dislocation and only one H center. Subsequent diffusion of V F centers away from dislocations and recombination with F centers results in the formation of stoichiometric divacancies thus providing a driving force for the formation and growth of vacancy voids observed experimentally.…”

“…the difference between F and H center fluxes), which depends on the difference between the void bias and the mean bias of the system for the absorption of F centers. This difference is positive for void radii lager than a critical radius, crit V R , which is determined by the ratio of material constants related to the void and dislocation biases [4]:…”

“…The critical void radius R V crit is given by the same equation (1) as the critical colloid radius, and it is smaller than the radius of void nuclei produced by bubble-colloid collisions [4,5]. Accordingly, one would expect all void nuclei to grow to visible sizes.…”

“…In the present paper, the exciton-induced emission of F-centers from colloids is taken into account in the calculation of colloid nucleation and growth rates in the framework of the modified rate theory [8]. The driving force of colloid growth is the large bias of halogen bubbles for absorption of H centers rather than the dislocation bias employed in the previous models [3,4]. Thus, radiolysis (separation of chlorine and sodium into bubbles and colloids) and the development of stoichiometric defects (voids and dislocations) occur simultaneously but relatively independently.…”