Commonalties of the influence of lower valent A-site and B-site modifications on lead zirconate titanate ferroelectrics
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Commonalties of the influence of lower valent A-site and B-site modifications on lead zirconate titanate ferroelectrics and antiferroelectrics Qi Tan, Z. Xu, and Dwight Viehland Department of Materials Science and Engineering, and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (Received 4 August 1997; accepted 7 May 1998)
Studies of the structure-property relations of lead zirconate titanate (PZT) modified with lower valent substitutions on the A- and B-sites have been performed as a function of substituent concentration. These investigations have yielded common changes induced by these substitutions on ferroelectric phases. The commonalties are the presence of fine domains and polarization pinning effects. Differences in domain morphologies were observed between the rhombohedral and tetragonal ferroelectric phases. Rhombohedral ferroelectrics were found to exhibit “wavy” domain patterns with increasing dopant concentrations, whereas a lenticular domain shape was preserved as the domain size was decreased for tetragonal ferroelectrics. These differences were explained in terms of different pinning mechanisms based on the differences in local elastic strain accommodations. Investigations of high Zr-content PZT have revealed that the ferroelectric rhombohedral phase becomes stabilized over the antiferroelectric orthorhombic with increasing concentrations of lower valent modifications. This change was explained in terms of the enhanced coupling between oxygen octahedra due to the bonding of oxygen-vacancy dipoles.
I. INTRODUCTION
Piezoelectric resonators and transducers are some of the most important applications of lead zirconate titanate (PZT) ceramics. One of the unique physical characteristics which makes PZT an excellent material for these applications is that it can be made electrically “hard” to polarization switching by appropriate compositional modifications. In addition, “hard” PZT’s have high mechanical quality factors. An interaction between substituents and domain boundaries is believed to be the origin of the “hard” switching characteristics. The effects of various substituents on the mechanical quality factor have previously been studied1–3 and explained in terms of the conventional Gerson model,4 i.e., the variation of domain mobility due to substituents correlated vacancies. Domain boundary pinning effects have been studied by Postnikov et al.5 using internal friction methods and by Carl and Hardtl6 using dielectric methods. Trapping of charge carriers at grain boundaries and domain boundaries has also been proposed to play both a stabilizing role7 and to result in enhanced fatigue characteristics.8,9 Furthermore, in recent years, multilayer devices based on morphotropic phase boundary (MPB) compositions of “hard” PZT ceramics have received special attention because of their excellent electromechanical behavior.10 –12 For these multilayer structures, the configuration and interaction of domains with subs
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