Structural damage in spinel after ion irradiation

Abstract

Monocrystalline MgAl 2O 4 spinel crystals were irradiated at 100 K with overlapping ion implantations: an initial implantation of 185 keV He + ions to 1.7 × 10 15 ions/cm 2, followed by a second implantation of 50 keV Ne + ions to 5 × 10 12 ions/cm 2. An additional set of spinel crystals was exposed only to the He implantation. Each irradiated sample was characterized by ion channelling and cross-sectional transmission electron microscopy. Defect clusters and dislocation loops were observed in each irradiated sample. The size of microstructural defects in the doubly ion-implanted sample was not increased compared to the He only ion implantation, and the density of defects in the doubly implanted sample actually decreased. These observations indicate that preexisting irradiation-induced interstitial defect clusters and Frank dislocation loops do not serve as effective sinks for interstitial point defects in spinel. Vacancy clusters (if they exist) probably are effective sinks for interstitials and to some extent, are erased by interstitials created during the second irradiation. These observations have important implications for understanding the role of defects in determining the properties of irradiated spinel.