|Title:||Investigation of microtexture in ferroelectric Pb2(Sc, Ta)O6 ceramics, piezoelectric Pb(Zrx, Ti1-x)O3 ceramics and films and a study of structural ordering in Pb2(Sc, Ta)O6|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xiii, 138,  leaves : ill. ; 30 cm|
|Abstract:||Crystallographic orientations of the various samples of polycrystalline lead scandium tantalate, Pb2(Sc,Ta)O6 abbreviated PST, were investigated by the technique electron backscatter diffraction pattern (EBSP) in the scanning electron microscope. The samples were processed under different conditions of temperature and annealing. Several hundreds of crystal orientations in the bulk ceramics were examined by EBSP and the results were plotted in microtexture pole- and inverse pole-figures for determination in order to their average preferred orientations. The results were compared with crystallographic information collected using X-ray diffraction. In addition, local textures and the misorientations between the nearest neighboring grains in certain selected regions in the PST ceramics were determined. The degree of structural ordering and the dielectric constant of each sample were measured and compared with their crystallographic textures. In order to compare the results with another lead-based ferroelectric ceramic, an unpoled and a poled tetragonal lead zirconate titanate (PZT) ceramics were examined. The overall and local textures of these ceramics were studied. The misorientations in grain-level were examined. The piezoelectric coefficient and the estimated degree of poling were measured. The change in crystallographic texture was detected, which was compared with the piezoelectric properties of the ceramics. The crystallographic texture of a PZT thin film was investigated by EBSP in the SEM. This PZT hetroepitaxial multilayer film was grown by pulsed-laser deposition method (PLD). The compositions of the various layers corresponded to Pb(Zr0.52Ti0.48)O3, La0.7Sr0.3MnO3 (LSMO) and LaAIO3 (LAO), which is the substrate. Highly oriented crystallographic texture was observed, which was represented in both microtexture pole- and inverse pole-figures. The structural ordering in B-site cations in Pb2(Sc,Ta)O6 was studied. The degree of order was measured using the intensities of the superstructure reflections (h+1/2, k+1/2, l+1/2) in the X-ray diffraction patterns. The structural ordered domains and their anti-phase boundaries were imaged using dark-field imaging by selecting the superstructure reflections in the TEM. Various sizes and shapes of the structural ordered domains were observed. In addition, high resolution TEM (HRTEM) images were recorded to show detailed features of the structural ordered domains and their anti-phase boundaries. A phenomenological approach, which utilizes the Monte Carlo method and the next-nearest neighbor Ising model, was proposed to simulate the structurally ordered domain in PST ceramics. Various degrees of short- and long-range order of the B-site cations, Ta and Sc, were recorded by the simulation methods. Although the preliminary model is simple, the simulated images that included structural ordered domains and their anti-phase boundaries correlated with the observations in TEM. This was especially relevant in the case involving the scheme of grain boundary diffusion.|
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