Kinetics of point defects in electron irradiated MgO

Abstract

Abstract The kinetic behavior of point defects in MgO has been studied through the observation of the nucleation and growth processes of dislocation loops during electron irradiation in a high voltage electron microscope. Results have been obtained on dislocation loop formation and growth in MgO single crystals obtained from three sources during irradiation at temperatures from 25 to 1000°C. Circular and elongated dislocation loops with 1 2 〈110〉 Burgers vectors lying on {110} planes are formed in Norton MgO and ORNL and Tateho MgO, respectively. The loop nucleation stage is complete early in the irradiation and the density of loops reaches a saturation value CL. The diameter of loops D increases with irradiation time t. The dependence of CL and D on t and electron flux φ at various temperatures T is expressed as follows: C L ∝ t 0 φ −1 2 and D ∞ t 1 2 − 2 3 at T ≲ 600° C and D tφ −1 2 at T ≳ 600° C . Experimental results below ≈ 600°C are successfully analyzed using a theory based on a nucleation mechanism controlled by interstitial motion in which one or two pairs of Mg- and O-interstitials serve as stable nuclei for interstitial loops. The growth kinetics of loops above ~ 600°C are understood in terms of the steady state behavior of interstitials and vacancies with high mobilities, and are controlled by the vacancy species (Mg or O), the product of whose mobility and displacement rate has the lower value.