Radiation Damage In BaTiO₃ Investigated By Computer Simulation

Perovskite ferroelectrics (ABO₃) are very important for a wide range of technological applications in optoelectronics, waveguides, laser frequency doubling devices, high capacity computer memory cells, etc. With the development of the computer technology, simulation method has been widely used to study the structure and properties of the perovskite-type ferroelectrics. Molecular dynamics (MD) simulation and Monte Carlo (MC)are the most important computer simulation techniques.BaTiO₃ is a kind of perovskite ferroelectrics which has the advantage of ferroelectric property, piezoelectric property and radiation resistance. BaTiO₃ thin films and devices have important application under strong irradiation. The structure damage, especially the oxygen vacancies have crucial influence on the response of ferroelectrics under radiation. The paper includes two parts of Molecular dynamics (MD) simulation and Monte Carlo(MC) simulation:(i)Molecular dynamics is applied to simulate formation and recovery process of defects in BaTiO₃ under the impact of primary knock-on atom (PKA). The results show that the initial movement direction and energy of PKA have significant influence on the number of defects, and the averaged threshold displacement energy of Ba, O and Ti atom is 69eV, 51eV and 123eV respectively. Afterwards, a certain kinetic energy was given to a Ti atom (PKA) in order to investigate the process of defect creation in BaTiO₃ crystal by displacement cascades over a wide range of primary knock-on atom (PKA) energy (1.5 keV <EPKA< 4.0 keV) .The results show that the initial orientation of the PKA has significant influence on the number of defects because of different collision type (glancing collisions or direct knocks). It is also illustrated that the number of defects does not simply increase with the increasing of PKA energy due to the annealing effect. The simulation provides a detailed description of the collision cascades to understand the radiation damage in BaTiO₃.(ii) Furthermore the SRIM code is applied to simulate the H+,O2- and Au²⁺ irradiation damage in BaTiO₃ thin film. The results show that the number of vacancy increases with increasing incident energy, but the speed of increase depresses, and the number of vacancy decreases obviously with increasing incidence angle when it is more than 70°. We select H⁺,O^2- and Au²⁺ in order to research the radiation damage by different kinds of ions. The results show that the number of vacancy created by Au²⁺ irradiation is far more than the other two. The reason is that nuclear stopping power of Au²⁺ is greater than two others in BaTiO₃ thin film. It results in a large number of Au²⁺depositting near the surface of BaTiO₃ and forming more defects. This dissertation investigates the dynamic process of defects in BaTiO₃ produced by radiation at atomic level. The simulation results have some significance to analyze the microstructure damage by ion radiation.