Ab initio pseudopotential study of vacancies and self-interstitials in hcp titanium

• Published in: Philosophical magazine (Abingdon, England) Vol. 89; no. 20; pp. 1629 - 1645
• Main Authors: Tunde Raji, Abdulrafiu, Scandolo, Sandro, Mazzarello, Riccardo, Nsengiyumva, Schadrack, Härting, Margit, Thomas Britton, David
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 11.07.2009; Taylor & Francis
• Subjects: ab initio; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Defects and impurities in crystals; microstructure; density-functional theory; Electron states; Exact sciences and technology; ion implantation; Methods of electronic structure calculations; Physics; point defects; residual stress; self-interstitial; Structure of solids and liquids; crystallography; Theories and models of crystal defects; titanium; Vacancies; Atomic position; Ab initio method; Pseudopotential; Interstitials; Energy barrier; APW calculations; Relaxation; Experimental result; Tetrahedral configuration; Diffusion barriers; Dumbbell model; Single atom; Interstitial impurities; Crystallographic site; Titanium; Divacancy; Ab initio calculations; Self-diffusion
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786430903019032

By means of an ab initio plane-wave pseudopotential method, monovacancy, divacancy and self-interstitials in hcp titanium are investigated. The calculated monovacancy formation energy is 1.97 eV, which is in excellent agreement with other theoretical calculations, and agrees qualitatively with published experimental results. The relaxation of the atoms around a single vacancy is observed to be small. Two divacancy configurations, the in-plane and the off-plane, have also been shown to be equally stable. With regards to the interstitials, of the eight configurations studied, two (octahedral and basal octahedral) have relatively lower formation energies and are, thus, the most likely stable configurations. We find small energy differences between them, suggesting their possible co-existence. It is also observed that the tetrahedral configuration decays to a split dumbbell configuration, whereas both the basal tetrahedral and the basal pseudocrowdion interstitials decay to the basal octahedral configuration. Using the nudged elastic band method (NEB), we determine a possible minimum energy path (MEP) for the diffusion of self-interstitial titanium atoms from an octahedral site to the nearest octahedral site. The energy barrier for this migration mechanism is shown to be about 0.20 eV.