Papers by Author: R. Edwin Garcia

Abstract: Our research investigates the correlations between domain texture and microstructural features, including crystallographic texture in bulk and thin film polycrystalline materials to understand the development of piezoelectric and other anisotropic properties in a number of rapidly evolving lead free piezoelectric materials. We investigate approaches to understanding polarization distributions by starting from polarization measurements. In addition, 2D and 3D microstructural simulations are carried out in all types of ferroelectrics to rationalize and then engineer their equilibrium and kinetic response. This paper discusses recent findings associated with bulk piezoelectricity, phase stability, and ferroelastic and ferroelectric domain motion for materials such as Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) and Bi_0.5Na_0.5TiO₃ (BNT). Conventional and synchrotron-based x-ray diffraction, electron and optical microscopy and piezoelectric characterization techniques are employed to assess texture, both as a function of poling and temperature. The coupling between microstructure and the inherent directional biases fundamental to piezoelectric and ferroelectric performance enable consideration of orientation and anisotropy in systems with unique constraints.

Abstract: In the last ten years of ongoing research in the modeling of polycrystalline ferroelectric ceramics a myriad of analytical and numerical implementations have emerged to predict and support the engineering of ferroelectrics in both its single-crystal and polycrystalline forms. Traditional atomistic approaches capture the intrinsic behaviors, and have led to great improvements in the chemistries of these systems. Similarly, macroscopic engineering approaches have focused on the development of phenomenological descriptions that capture the empirical static and time-independent behavior. At the interface of these two apparently divorced approaches, thermodynamic-based microstructural evolution descriptions inspired in phase field models have risen as the necessary link between the atomic and macroscopic levels. This new and emerging methodology starts from the predicted behaviors given by their atomic counter-parts, and resolves the effects of grain boundaries, and de-convolves the grain-grain mesoscopic interactions. Much of the future of ferroelectrics lies in the delivery of improved chemistries and microstructures, and on bridging the understanding currently existing atomistic and continuum descriptions. Overall, it is expected that current and emerging technological challenges will be the driving force to minimize ferroelectric fatigue and realize lead-free materials with performances close to currently existing (lead containing) ones. Moreover, it is expected that while an accurate understanding of the intrinsic properties of materials are key to define improved ferroelectric solids, it will be the detailed understanding of the extrinsic response of ferroelectric materials, in both bulk and thin film form, that will take these materials to reach the highest performances possible.