Date of Award
Doctor of Philosophy
Materials Science and Engineering
William J. Weber, Maik K. Lang, Yanfei Gao
Ab initio molecular dynamics (AIMD) was utilized to test a series of materials, MgO, LiNbO3 , and LiTaO3 , to determine defect structures produced due to low energy recoil events . The kinetic energy required to displace an atom from its lattice site, the threshold displacement energy, was calculated for an array of directions in each material, based on symmetry and complexity of the structure. MgO having a simple rock salt structure provided a model material for demonstrating computational techniques used later on LiTaO3 and LiNbO3 . The minimum values for displacing an atom were at 25.5 eV for O and 29.5 eV for Mg. For LiNbO3 and LiTaO3, the minimum energy for displacing an atom was 6 eV for Li in LiTaO3 and 14 eV for Li in LiNbO3 . Average values for threshold displacement energies agreed well with those used in calculations, but they have not yet been accurately measured experimentally. Additionally, the defect structures and properties were identified and reported as a result of the simulations. The high defect formation energy reported for cation vacancies means that they are unstable in the structure and will either recombine, form defect complexes, or migrate to defect sinks in the material.
Petersen, Benjamin Aaron, "Low Energy Recoil Simulations in MgO, LiNbO3, and LiTaO3 Using Ab Initio Molecular Dynamics. " PhD diss., University of Tennessee, 2017.