Defect structure of oxygen-vacancy clusters in O18 and self ion implanted Fe(100) crystal by ion channeling and ab-initio study

Abstract

Lattice site position of O18 in the presence of vacancy defects in Fe(100) crystal is measured by ion channeling and the corresponding oxygen-vacancy cluster configuration is predicted with Density Functional Theory (DFT) calculations. Energy dependent dechanneling and Slow Positron Doppler broadening analysis show the defects to be vacancy dislocation loops. In O18 ion implanted Fe, O18 is found to be in tetrahedral interstitial position. If self ion is irradiated together with O18 to increase vacancy defects, O18 is found to be trapped at 1.2 Å away from the lattice position along <111>. From DFT calculations, similar lattice site of O is predicted with a displacement of 1.1 Å along <111> for the interaction of oxygen with ½ <111> vacancy loop structure. Upon increasing vacancy defects further by increasing the fluence of self ions, O18 is found to shift near octahedral interstitial site displaced by 0.6 Å along <100>. DFT calculations show a similar displacement of 0.46 Å along <100> for the interaction of oxygen with <100> vacancy loop structure. Our combined experimental and DFT studies provide strong evidence of O trapping at vacancy dislocation loops and O trapping site is sensitive to ½ <111> and <100> type vacancy dislocation loops.