X-ray diffraction and high-resolution transmission electron microscopy study on A -site ordering of lanthanum-modified l
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The ordering behavior of La-modified lead zirconate titanate relaxor (PLZT 9/65/35) was investigated by use of an x-ray diffractometer (XRD) and high-resolution transmission electron microscopy (HRTEM). It was shown that a {h + 1/2, k + 1/2, 0}-type superlattice exists both in the x-ray diffraction pattern and selected area electron diffraction (SAED) image. High-resolution electron micrographs further demonstrated the existence of the superlattice and exposed the ordered and disordered regions in the lattice level. A model referring to an A-site body-centered pseudo-cubic superstructure was proposed.
Relaxors are characterized by diffuse phase transition (DPT) and a strong frequency dispersion of the dielectric maxima. Smolenskii1 originally proposed that it was a chemical inhomogeneity on a cation site giving rise to a diffuse phase transition. The degree of diffuseness would thus be expected to depend upon the randomness of the composition fluctuations. This was confirmed by Setter and Cross, 23 who found that the phase transition in Pb(Sci/2Tai/2)O3 (PST) was sharper when 5-site cation ordering was increased by thermal treatment. With the development of microscopic techniques, especially as the TEM was used, many previously accepted disordered compounds were found to be ordered on the nanoscale.4 Randall et al.5 subsequently proposed that it is the scale of the inhomogeneity that determines the relaxor behavior. They suggested a classification of the complex lead perovskites with A(B'B")O3 structure, and pointed out that complex perovskites possessing no detectable order (
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