Structure and Mobility of Defects Formed from Collision Cascades in MgO

We study radiation-damage events in MgO on experimental time scales by augmenting molecular dynamics cascade simulations with temperature accelerated dynamics, molecular statics, and density functional theory. At 400 eV, vacancies and mono- and di-interstitials form, but often annihilate within milliseconds. At 2 and 5 keV, larger clusters can form and persist. While vacancies are immobile, interstitials aggregate into clusters (I_n) with surprising properties; e.g., an I₄ is immobile, but an impinging I₂ can create a metastable I₆ that diffuses on the nanosecond time scale but is stable for years.