Microstructure-Controlled Multilayer PZT Actuators: Effects of Cyclic Actuation on Crystallographic Structure
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Microstructure-Controlled Multilayer PZT Actuators: Effects of Cyclic Actuation on Crystallographic Structure* Jens Müller1, Stephanie A. Hooker1, and Davor Balzar1,2 1 Materials Reliability Division, National Institute of Standards & Technology (NIST), 325 Broadway, Boulder, CO 80305-3328 2 Department of Physics and Astronomy, University of Denver, Denver, CO 80208 ABSTRACT In this study, multilayered PbTixZr1-xO3 (PZT) samples (produced at sintering temperatures in the range of 1175 °C to 1325 °C) were electrically fatigued by long-term exposure (~106 cycles) to electric fields, and the parameters of initial and remnant polarization were estimated. Changes in the crystallographic microstructure as a function of sintering temperature TS were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to gain insight on fatigue mechanisms and their prevention. Results showed that domain wall movement was facilitated in samples processed at TS less than 1250 °C, and that such samples were more resistant to electrical fatigue.
INTRODUCTION The ongoing development of new applications that make use of piezoelectric ceramics, including adaptive structures, vibration isolation, and nanorobotics, demands smaller, highly reliable devices that are fatigue resistant under long-term use. In order to achieve maximum displacement in these instances, actuators will be operated with electric fields higher than those in conventional applications. However, under such harsh driving conditions, an increased degradation in ferroelectric properties is observed. Tailoring the ceramic microstructure by controlled sintering offers one possible route to improve fatigue resistance. EXPERIMENTAL DETAILS Samples were prepared by multilayer fabrication using commercially available submicrometer sized PZT-5A powder [1]. Platinum (Pt) electrodes were embedded in the material between the layers with a spacing of 50 µm to 60 µm, as shown in Figure 1a. The Curie temperature, TC, of our material is 320 °C [2]. During annealing at temperatures above TC the unit cells possess a paraelectric face-centered cubic structure. Once a sample temperature dropped below TC after the annealing process, the material underwent a spontaneous distortion (Curie transition) into the face-centered tetragonal structure. The displacement of ions resulting from the cell distortion creates a polar axis, aligned with the long crystallographic c-axis, which gives the material its ferroelectric properties. *
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Three different sample sets were examined in this study. Every set consisted of seven samples, with each sample annealed at a different sintering temperature TS for 24 minutes. Sintering temperatures ranged from 1175_°C to 1325_°C. The different sets are defined as follows: Set 1 is referred to as “as-produced”, meaning that the only difference between the samples of this set was the sintering temperature TS. The microstructure res
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