Domain structure-property relations in lead lanthanum zirconate titanate ceramics
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Domain structure-property relations in lead lanthanum zirconate titanate ceramics Mehmet A. Akbas,a) Ian M. Reaney, and William E. Lee Department of Engineering Materials, The University of Sheffield, Sheffield, S1 3JD, United Kingdom (Received 1 August 1995; accepted 15 May 1996)
The domain structure and dielectric properties as a function of lanthanum concentration and ZryTi ratio have been investigated in rhombohedral and tetragonal lead lanthanum zirconate titanate (PLZT) ceramics. Transmission electron microscopy revealed that, with increasing lanthanum concentration and ZryTi ratio, the long-rangeordered domains (macrodomains) reduced in width, initially being fine scale (20 nm) striations, but eventually forming a “mottled” contrast (5 nm), characteristic of a relaxor. Relative permittivity measurements as a function of temperature revealed a correlation between broadening of the dielectric maxima and the onset of relaxor-type behavior with the appearance of the striations and mottled (relaxor) contrast, respectively.
I. INTRODUCTION
Thin polished plates of lead lanthanum zirconate titanate (PLZT), perovskite ceramics, have high optical transparency and exhibit excellent electro-optical characteristics1 so that many applications have been proposed in the field of electro-optics, such as optical shutters, light modulators, memories, and display devices.2 By changing the lanthanum concentration in PLZT ceramic from low (4 mol %) to high (10 mol %) values for fixed ZryTi ratios, it is possible to get a smooth transformation from ferroelectric to relaxor and then to paraelectric behavior.2 Moreover, the ferroelectric (FE) phase may be stabilized either in the tetragonal or rhombohedral crystal structures, depending on the ZryTi ratio.2 Therefore, PLZT ceramics are ideal for characterizing and comparing the domain structure observed in ferroelectric and relaxor ceramics. Recently, several authors have observed spontaneous transformation from relaxor to ferroelectric as a function of decreasing temperature in Pb-based perovskites using in situ transmission electron microscopy (TEM).3–7 The transition was revealed as a sudden loss of mottled contrast and the appearance of ferroelectric macrodomains. It has also been shown that such changes are also present as a function of composition in PLZT,6,8,9 but to date no comprehensive study has been carried out, varying both La concentration and Zr : Ti ratio close to the morphotropic phase boundary. Furthermore, previous work has been carried out using ceramics prepared by conventional mixed oxide routes that are prone to compositional variations of the same order as the grain size.
a)
Current address: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272. J. Mater. Res., Vol. 11, No. 9, Sep 1996
The present work characterized the domain structure as a function of composition in PLZT ceramics close to the morphotropic phase boundary and related to the results to
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