Effects of residual (or internal) stress on ferroelectric domain wall motion in tetragonal lead titanate
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Alexander H. King Ames Laboratory, Ames, Iowa 50011
Keith J. Bowmana) Purdue University, West Lafayette, Indiana 47907 (Received 2 July 2008; accepted 11 February 2009)
The effect of temperature on grinding-induced texture in tetragonal lead titanate (PT) has been investigated as a function of the magnitude of loading applied to the sample surface during grinding, using in situ x-ray diffraction (XRD) with an area detector. Compared to the ground PT under lower loading conditions (5 N), the ground PT under higher loading conditions (40 N) retains strong ferroelastic texture near the Curie temperature (TC) around 350 C and undergoes smaller changes in lattice parameter or tetragonality versus temperature during in situ thermal cycling between room temperature and approximately 100 C above the TC. Inhibited depoling of ground PT materials investigated by in situ texture measurements demonstrates the effects of residual stresses.
I. INTRODUCTION
Understanding the effects of stresses on domain wall motion resulting in ferroelastic textures is essential to fostering a deeper understanding of microstructure and thin film effects that determine the performance of piezoelectric materials. The internal stresses within a grain are in part determined by the overall stress state of an assemblage of grains within a material. Altering the stress state by the introduction of near-surface residual stresses through grinding is one approach for producing ferroelastic textures in piezoelectric materials. Unlike a crystallographic texture that typically describes a preferred orientation of the crystals at all temperatures, a ferroelastic texture is thereby a bias of the domain structure within individual crystals favoring specific ferroelastic variants within each grain based on its orientation and interactions with neighboring grains. The orientation distribution of these variants from domain wall motion results in a ferroelastic texture. Grinding is a convenient means of generating controllable amounts of surface stresses, and our focus is on the grains that are oriented so as to be maximally affected in the anisotropic stress state generated by surface grinding, i.e., the 200 and 002 x-ray diffraction (XRD) peaks. We previously reported1 that ground PT and soft lead zirconated titanate (PZT) materials retain strong ferroelastic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0218 J. Mater. Res., Vol. 24, No. 5, May 2009
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textures during thermal cycling, even after excursions to temperatures slightly above the Curie temperature (TC) where these materials would normally be expected to transform from tetragonal to cubic. The residual stress caused by grinding delayed the onset of the phase transition, especially in PT. In the previous work, we explained the inhibited depoling behavior of ground materials as a result of interactions between grinding-induced residual stresses and the internal stresses deriving from domain
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