Papers by Author: William F. Shelley

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.

Abstract: Determination of the domain textures in many lead zirconate titanate (PZT) piezoelectrics can be complicated by the presence of second phases, internal strains and small differences in lattice parameters for the commonly used 002 and 200:020 peaks. The domain texture is influenced by the applied polarization necessary for these materials to demonstrate piezoelectricity. In this paper we explore the use of 022:202 and 220 peaks for evaluating the domain textures and helping resolve the complexities of texture analysis in the presence of multiple phases. The two materials explored in this paper include a nominally single phase tetragonal PZT material and a mixed phase tetragonal-monoclinic lead magnesium niobate (PMN)-PZT alloy.