This theoretical research will build a program aimed at investigating defects in ferroelectrics and revealing their effects on local and ground-state structures, phase transitions, dielectric and electromechanical responses; determining and understanding the properties of ferroelectric thin films; and, designing new ferroelectrics with optimal and/or original properties. The research program is integrated with the educational experiences of students.
The research objectives will be achieved through the development and/or use of the following state-of-the-art and ab initio numerical tools: accurate first-principles techniques, including total energy calculations, computation of phonon spectrum, modern theory of polarization and electric-field effects; effective Hamiltonian approaches that will extend the reach of first-principles calculations by realistically mimicking defects in perovskites and/or ferroelectric thin films at finite-temperature; and the inverse method that allows an efficient design of materials with improved properties. Collaborations with well-known European groups and industries having a vital experimental or applied program in ferroelectrics will be strengthened.
The cooperative activities between Arkansas and its European partners will allow a careful comparison between predictions and measurements, which is important to fully understand the systems to be investigated, and to refine the numerical tools to be developed (if needed). Many defects and thin films, and their effects on properties, are going to be investigated. Examples include chemically-ordered nanoscale regions in relaxors, oxygen vacancies in BaTiO3, Pb vacancies and Pb misplaced on B sites in Pb(Sc,Nb)O3, La dopants in Pb(Zr,Ti)O3, and (parasitic) pyrochlore phases. Other examples are the dependencies of the phase transitions sequence and nature (i.e., normal vs. diffuse) of BaTiO3 thin films on their thickness, surface termination, growth orientation, substrate, pressure, mechanical boundary conditions and electric fields. Particular emphasis will be put on determining how some striking features known to occur in some bulk materials, - e.g., quantum effects in KtaO3, monoclinic phase and antiferrodistortive displacements in Pb(Zr,Ti)O3, and the role of internal electric field and atomic ordering on properties of Pb(Sc,Nb)O3 - evolve when going from bulk to thin films. New phenomena and optimization of piezoelectric and dielectric properties are also expected to be discovered by playing with the (atomic and film-related) degrees of freedom in Pb(Sc,Nb,Ti)O3 thin films.
A broad knowledge of perovskites containing defects, and of ferroelectric thin films, will be gained thanks to the diversity of techniques to be used and the variety of systems to be investigated. In addition, to build a network that will be the basis for future collaboration and exchange of students between the involved institutions, the collaborative efforts have also the potential to result in the realization of devices with improved and/or new functionalities, and that will positively affect quality of life and improve safety. A website will report a database related to the findings, and will provide the codes to be developed during the project. In addition, students will be trained at all levels. %%% This theoretical research program investigates new ferroelectric materials and thin films formed from these materials. Ferroelectric materials are unique in their ability to create a spontaneous polarization when certain conditions are met. This makes the materials particularly useful in a variety of applications. The proposed program has an extensive international collaboration with groups in Europe. Students will participate in the research at all levels. ***
