Relaxor ferroelectric systems (bulk/nanostructure) are very important because of their unusual properties and potential applications [1,2]. Atomistic simulations can reveal many interesting features of bulk or nanostructured materials that may lead to new applications [3,4]. In this study, Monte-Carlo (MC) and Molecular Dynamics (MD) methods, within the framework of Effective Hamiltonian (Heff), are used to simulate Pb(Mg1/4Nb1/2Ti1/4)O3 nanodots (PMN-25PT NanoDot) for various cases, such as the size of nanodots and the distribution of B-site atoms. We summarize our work as the follows. First, we extend the Heff developed in reference [5] to include the influence of surfaces by adding terms that characterize the interaction of surfaces with local dipoles and strains. Second, we perform MC and MD simulations under ideal open circuit condition from high to low temperature for various nanodots. During each simulation, the size of dots, the distribution of B-site atoms, and the temperature are kept fixed. The outputs of our simulations are local mode u (which are directly proportional to polarizations) and strains. Third, we compute static/dynamic dielectric susceptibilities, toroidal and hyper-toroidal moments as well as their susceptibilities using the methods shown in reference [6]. Results of these MC/MD simulations reflect the importance of the size of nanodots and the distribution of B-site atoms. These results will be discussed in details.
This work is supported by King Abdulaziz City for Science and Technology under grant number 11-NAN1414-10 and ONR Grant N00014-12-1-1034.