The relative contribution of ferroelastic and ferroelectric texture to the character of a hard PZT ceramic

Thomas Stallings Key, Purdue University

Abstract

The development of ferroelastic (90°) texture in addition to ferroelectric (180°) texture is essential to maximizing the piezoelectric properties of many hard tetragonal PZTs, including Piezoetechnologies K270. Ferroelastic texture results from motion of domain walls that is dependent on an individual crystals orientation. Increases in ferroelastic texture raises the maximum net polarization that can be achieved by changes in ferroelectric texture. By studying a hard PZT poled under various temperature conditions, insight was gained into factors affecting the development of ferroelastic texture and how ferroelastic texture contributes to piezoelectric properties. Depinning proved to be the major barrier to preventing ferroelastic domain wall motion where strain based domain interactions and polar defect complexes on the domain level appear to be the dominant factors. Insight into the affect of increased domain texture on the relationship between the increasing magnitude of the remnant polarization (:Pr:) and the magnitude of the coercive field (:EC:) was gained by plotting :EC: vs. :Pr: as a function of poling time for a variety of poling temperatures. At low :Pr: values, :EC: increased rapidly as a function of increases in :Pr: regardless of the poling temperature. This relationship was characteristic of samples poled at 25 °C where increases in ferroelastic texture were largely suppressed. Because increases in polarization were still observable changes in ferroelectric texture most responsible for the polarization increase and like play a strong role in the initial :EC: vs. :Pr: relationship. As :Pr: increased beyond 5 to 8 ìC/cm2, the slope of :EC: vs. :Pr: decreased where the reduction in slope increased with poling temperature. This only occurred in samples poled at elevated temperatures where ferroelastic texture was know to ultimately develop during the poling process, leading to the suggestion that the change in slope was due to increases in combined ferroelectric and ferroelastic texture. Lastly, it was found that electric field induced increases in ferroelectric texture by poling at 25 °C occurs while ferroelastic domain wall motion is largely suppressed. This change in ferroelectric texture severely hinders the rate at which subsequent ferroelastic domain wall motion can be induced during poling at elevated temperatures below TC, suggesting that hard PZT samples should be preheated to the poling temperature before poling begins.^

Degree

Ph.D.

Advisors

Keith J. Bowman, Purdue University.

Subject Area

Engineering, Materials Science

COinS