Papers by Author: Jacob L. Jones

Abstract: Ferroelectric/ferroelastic structures exhibit systematic crystallographic distortions below certain phase transition temperatures. Domains, or regions of spatial continuity in such distortions, form in a self-compensating pattern when cooled in the absence of an applied field, forming equal volume fractions of all possible states by uniform selection of crystallographic variants. An applied field (poling) can alter the volume fraction of domains within the ferroelectric phase by switching of the non-preferred orientations, a form of ferroelectric domain texture. When ceramics possess a crystallographic texture prior to inducing domain texture, the two component textures combine multiplicatively to form the complete product texture. Using tape cast bismuth titanate (Na0.5Bi4.5Ti4O15) with an initial crystallographic texture, this paper establishes the quantitative approach for resolving both the component grain and domain textures and describing the complete product texture.

Abstract: The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.