Availableonlineatwww.sciencedirectcom ScienceDirect 98 Acta materialia ELSEVIER Acta Materialia 55(2007)5538-5548 Crack tip process zone domain switching in a soft lead zirconate titanate ceramic Jacob L. Jones, S. Maziar Motahari, Mesut Varlioglu, Ulrich Lienert Joel v bernier. mark hoffman ersan ustundas Department of Materials Science and Engineering, P.O. Box 116400, Unicersity of Florida, Gainesville, FL 32611-6400, USA Department of Materials Science and Engineering, 2220 Hooter Hall, lowa State University, Ames, IA 50011-2300, USA c Adranced Photon Source, Argonne National Laboratory, Building 401, 9700 S. Cass Avenue, Argonne, IL 60439, USA d School of Materials Science and Engineering, The University of New South Wales, NSW 2052, Australia Received ll January 2007: received in revised form 8 June 2007: accepted 8 June 2007 Available online 30 july 2007 Abstract Non-180 domain switching leads to fracture toughness enhancement in ferroelastic materials Using a high-energy synchrotron X-ray source and a two-dimensional detector in transmission geometry, non-180 domain switching and crystallographic lattice strains were measured in situ around a crack tip in a soft tetragonal lead zirconate titanate ceramic. At Ki=0.71 MPa m"and below the initiation toughness, the process zone size, spatial distribution of preferred domain orientations, and lattice strains near the crack tip are a strong function of direction within the plane of the compact tension specimen. Deviatoric stresses and strains calculated using a finite element model and projected to the same directions me sured in diffraction correlate with the measure ed spatial distributions and direction o 2007 Acta Materialia Inc. Published by Elsevier reserved Keywords: Ferroelectricity: Fracture; Ceramics: Toughness; X-ray diffraction(XRD) 1. Introduction depressions that result from the strain associated with fer roelastic switching perpendicular to the sample surface The inherent brittleness of ferroelectric ceramics is a [8, 9]. In electrically poled lead zirconate titanate(PZT) structural liability that leads to crack initiation at defects ceramics, Lupascu and co-workers showed that the change and stress concentrations such as pores and electrode and in potential energy can be mapped spatially surrounding substrate interfaces. However, non-180 domain switching the crack tip using a liquid-crystal display [2, 6]. Employing in the frontal zone and crack wake lead to a rising R-curve X-ray diffraction, Glazounov et al. [5] measured the inten behavior, or an increase in toughness with crack extension sity ratio change of certain diffraction peaks as a function [I-10]. Using various techniques, recent work has elicited of distance from the crack face. Hackemann and Pfeiffer the region in which domain switching occurs or the [7] have also demonstrated that domain orientations per- switching zone"in ferroelastic materials, the size of which pendicular to the sample surface can be measured around is related to the toughness er nhancement In BaTiO3 ceram- the crack tip using a small beam size from laboratory X ics, Nomarski interference contrast and atomic force rays in reflection geometry microscopy have been employed to measure local surface However, non-180 domain switching within the plane of the sample has yet to be reported, and it is this plane that or Tel: +1352 846 3788: fax: +1352 846 3355. exhibits a complex stress distribution contributing to the E-mail address: jones(@mse ufl.edu(J. L. Jones) toughness enhancement. The directionally dependent 1359-6454/30.00@ 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved dor: 10.1016/j. actamat. 2007.06.012Crack tip process zone domain switching in a soft lead zirconate titanate ceramic Jacob L. Jones a,*, S. Maziar Motahari b , Mesut Varlioglu b , Ulrich Lienert c , Joel V. Bernier c , Mark Hoffman d , Ersan U¨ stu¨ndag b a Department of Materials Science and Engineering, P.O. Box 116400, University of Florida, Gainesville, FL 32611-6400, USA b Department of Materials Science and Engineering, 2220 Hoover Hall, Iowa State University, Ames, IA 50011-2300, USA c Advanced Photon Source, Argonne National Laboratory, Building 401, 9700 S. Cass Avenue, Argonne, IL 60439, USA d School of Materials Science and Engineering, The University of New South Wales, NSW 2052, Australia Received 11 January 2007; received in revised form 8 June 2007; accepted 8 June 2007 Available online 30 July 2007 Abstract Non-180 domain switching leads to fracture toughness enhancement in ferroelastic materials. Using a high-energy synchrotron X-ray source and a two-dimensional detector in transmission geometry, non-180 domain switching and crystallographic lattice strains were measured in situ around a crack tip in a soft tetragonal lead zirconate titanate ceramic. At KI = 0.71 MPa m1/2 and below the initiation toughness, the process zone size, spatial distribution of preferred domain orientations, and lattice strains near the crack tip are a strong function of direction within the plane of the compact tension specimen. Deviatoric stresses and strains calculated using a finite element model and projected to the same directions measured in diffraction correlate with the measured spatial distributions and directional dependencies. Some preferred orientations remain in the crack wake after the crack has propagated; within the crack wake, the tetrag￾onal 0 0 1 axis has a preferred orientation both perpendicular to the crack face and toward the crack front. 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Ferroelectricity; Fracture; Ceramics; Toughness; X-ray diffraction (XRD) 1. Introduction The inherent brittleness of ferroelectric ceramics is a structural liability that leads to crack initiation at defects and stress concentrations such as pores and electrode and substrate interfaces. However, non-180 domain switching in the frontal zone and crack wake lead to a rising R-curve behavior, or an increase in toughness with crack extension [1–10]. Using various techniques, recent work has elicited the region in which domain switching occurs or the ‘‘switching zone’’ in ferroelastic materials, the size of which is related to the toughness enhancement. In BaTiO3 ceram￾ics, Nomarski interference contrast and atomic force microscopy have been employed to measure local surface depressions that result from the strain associated with fer￾roelastic switching perpendicular to the sample surface [8,9]. In electrically poled lead zirconate titanate (PZT) ceramics, Lupascu and co-workers showed that the change in potential energy can be mapped spatially surrounding the crack tip using a liquid-crystal display [2,6]. Employing X-ray diffraction, Glazounov et al. [5] measured the inten￾sity ratio change of certain diffraction peaks as a function of distance from the crack face. Hackemann and Pfeiffer [7] have also demonstrated that domain orientations per￾pendicular to the sample surface can be measured around the crack tip using a small beam size from laboratory X￾rays in reflection geometry. However, non-180 domain switching within the plane of the sample has yet to be reported, and it is this plane that exhibits a complex stress distribution contributing to the toughness enhancement. The directionally dependent 1359-6454/$30.00 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2007.06.012 * Corresponding author. Tel.: +1 352 846 3788; fax: +1 352 846 3355. E-mail address: jjones@mse.ufl.edu (J.L. Jones). www.elsevier.com/locate/actamat Acta Materialia 55 (2007) 5538–5548