Direct observation of polar nanostructures in PLZT ceramics for electrooptic applications
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Direct observation of polar nanostructures in PLZT ceramics for electrooptic applications V. V. Shvartsman1, A. Orlova2, D. Kiselev2, A. Sternberg3, and A. L. Kholkin1 1
Department of Ceramics and Glass Engineering and Center for Research in Ceramic and Composite Materials (CICECO), University of Aveiro, 3810-193 Aveiro, Portugal 2 Department of Physics, Tver State University, 170000 Tver, Russia 3 Institute of Solid State Physics, University of Latvia, LV-1063 Riga, Latvia
ABSTRACT Transparent Pb1-yLay(Zr1-xTix)1-y/4O3 (PLZT, y=0.0975, x=0.35) ceramics prepared via hot pressing techniques were studied via piezoelectric force microscopy (PFM). Clear piezoelectric contrast is observed in a cubic relaxor phase indicating spatial distribution of polarization with an average cluster size of about 50 nm. The irregular polarization pattern is associated with the formation of a glassy state, where random electric and stress fields are responsible for the disruption of the long-range ferroelectric order. Local poling of the ceramics resulted in the formation of a stable micron-size domain that could be continuously switched under varying dc bias (local hysteresis loop). The applied voltage of 10-12 Volts was enough to switch relaxor into the ferroelectric state. Fractal and correlation analysis of the observed images is presented. The fractal dimension close to 1.55 is consistent with the random distribution of charge defects in this material. The nature of the observed phenomena is discussed based on the current understanding of relaxor state in PLZT and possible effect of PFM instrumentation.
INTRODUCTION Ceramics of solid solution Pb1-yLay(Zr1-xTix)1-y/4O3 (PLZT) with high La content (>9 at%) exhibit remarkable dielectric properties and hysteresis-free electromechanical strain that make these materials promising for various applications [1]. Especially important is that these ceramics can be made fully transparent and thus useful for optical and photonic devices (e.g., due to their strong quadratic electrooptic effect). From the scientific point of view, most attention was paid to the relaxor properties of PLZT that are likely to be responsible for their superb dielectric, electrooptic and electromechanical performance. It was suggested that, due to La doping and formation of A- and B-site vacancies, the long-range ferroelectric order is disrupted and macroscopic domains do not form in the relaxor state. Instead, the polar nanoregions (PNRs) with the short-range order may appear in these materials even at the temperatures far above the maximum of dielectric permittivity. As was shown by Dai et al [2], with increasing La content, the micron-sized domains progressively change to tweedlike precursors and finally to PNRs that could not be directly observed because of their small size and dynamic character [3]. Contrary to "normal" ferroelectrics the polar configurations in relaxors are much less studied and understood. PLZT ceramics with the composition y=0.35 and La content > 9 at % show pronounced relaxor prope
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