The effect of ferroelastic coupling in controlling the abnormal aging behavior in lead magnesium niobate-lead titanate r
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The effect of ferroelastic coupling in controlling the abnormal aging behavior in lead magnesium niobate-lead titanate relaxor ferroelectrics Q. M. Zhang, J. Zhao, T. R. Shrout, and L. E. Cross Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 26 January 1996; accepted 27 December 1996)
The abnormal aging behavior, i.e., severe aging in the electric field induced piezoelectric coefficient while very weak dielectric aging, observed in the relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) ceramics under a dc electric bias field, can be significantly reduced by hot isostatic pressing (HIP) treatment on presintered samples. The aging can also be reduced by doping suitable amounts of either La (donor) or Mn (acceptor). We suggest that the reduction in the aging is due to the introduction of additional random fields into the material, which reduces the probability of the growth of micropolar regions into metastable and/or stable macropolar domains. The abnormal aging behavior and the effectiveness of HIP in reducing it indicate the importance of the elastic energy in controlling the aging and relaxor behavior in PMN-PT relaxor ferroelectrics.
I. INTRODUCTION
Aging or the change of the material properties with time is of great concern in many areas of application for ferroelectric ceramics. In the past decade, there were many experimental investigations devoted to the aging phenomena in the relaxor ferroelectric materials, especially in PMN-PT (Pb(Mg1/3 Nb2/3 )O3 –PbTiO3 ) and PLZT (lanthanum modified lead zirconate titanate) solid solution systems.1–4 The objective of these investigations was to identify the basic mechanisms associated with aging phenomena so that they can be minimized and also to elucidate the polarization mechanism in this class of materials. From those investigations, it was found that aging in PMN-PT and PLZT exhibits quite different behaviors compared with those in normal ferroelectric ceramics such as barium titanate and lead zirconate titanate and is more complex.5 For instance, as revealed by several recent experiments, aging of the dielectric behavior in PMN-PT depends strongly on the frequency and occurs even at temperatures where the material is in the pseudo-cubic phase (nonferroelectric phase). In addition, aging was found to be not log linear with time, but follows a time dependent curve of stretched exponential type: d d` 1 d1 exp f2stytdy g
(1)
where t is the aging time, d1 represents the part of the material constant varying with time and d` is the time independent part, and t measures the aging rate. Hence, the ratio of d1yd` in Eq. (1) is a measure of the degree (or amount) of aging in the corresponding property.6,7 Equation (1) describes a relaxation process J. Mater. Res., Vol. 12, No. 7, Jul 1997
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with a broad distribution of relaxation times and a smaller y sy < 1d corresponds to a broader distrib
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