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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/5058

Title: New perspectives on the phase transformations and properties in La-doped Pb(Zr, Sn, Ti)O3
Other Titles: La-shen za Pb(Zr, Sn, Ti)O3 de xiang bian ji qi te xing zhi zhan xin tou shi
La-滲雜 Pb(Zr, Sn, Ti)O3 的相變及其特性之嶄新透視
Authors: Chan, Wai Hung (陳偉紅)
Department: Dept. of Physics and Materials Science
Degree: Doctor of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Composite materials -- Analysis
Notes: CityU Call Number: QD139.P6 C43 2006
Includes bibliographical references (leaves 207-215)
Thesis (Ph.D.)--City University of Hong Kong, 2006
xvi, 219 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Antiferroelectric (AFE) lead lanthanum zirconate stannate titanate (Pb,La(Zr,Sn,Ti)O3, PLZST) is an attractive material system with promising properties as an alternative to ferroelectric (FE) and other dielectrics for device applications. The aim of this study was to improve the properties as well as to understand the phase transformation behaviours and the underlying mechanisms of this material system in both bulk ceramic and thin-film forms. It was found that a “soft” AFE PLZST ceramic with an AFE-to-FE switching field below the electrical breakdown limit could be prepared with 2 mol% lanthanum in a base FE lead zirconate stannate titanate ((Pb(Zr,Sn,Ti)O3, PZST) matrix located near the AFE/FE morphotropic phase boundary. The studied AFE PLZST system was shown to be of an incommensurate AFE orthorhombic structure instead of the previously reported tetragonal structure. In addition, the temporal effect of low temperature FE behaviours in AFE Pb0.97La0.02(Zr0.60Sn0.30Ti0.10)O3 ceramic was observed for the first time, which could be explained using a glass-like relaxation model. The macroscopic and microscopic studies confirmed that the dominant phase of the Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 ceramic was AFE at room temperature instead of FE, which is in disagreement with the previous reports. However, the electric-field-induced FE state of this ceramic had a very long lifetime at T<60 oC. In addition, the poled sample exhibited a low dissipation factor, a large transient pyroelectric coefficient and an excellent DC tunability at the FE-to-AFE transformation temperature for thermal sensing applications. Thin-film samples of the same nominal composition as Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 ceramic were also fabricated using a simplified sol-gel process. These films grown on (111)Pt/Ti/SiO2/Si substrates did not show any temporal FE behaviour at room temperature and generally had poorer electric properties than bulk ceramics. The microstructure of the annealed films could be completely changed by altering the thermodynamic barriers for nucleation or/and the pre-annealing temperatures. Furthermore, it was found that the sol-gel derived Pb0.97La0.02(Zr0.75Sn0.16Ti0.09)O3 films grown on (100)LaNiO3/Pt/Ti/SiO2/Si substrates had superior properties when they were pre-annealed at 500 oC. Their DC tunable pyroelectric behavior in the AFE films had been studied for the first time. Attempts were made to explain these observations using the existing models. In addition, highly (111)-oriented AFE PLZST films were successfully prepared on (111)Pt/Ti/SiO2/Si substrates by the radio frequency (RF) magnetron sputtering techniques. These films were found to have a single perovskite phase and a dense columnar microstructure with excellent electrical properties, such as high dielectric constant, low loss, high saturation polarization of ~70 μC/cm2, etc., after post-annealing at 700 oC for 30 min.
Online Catalog Link: http://lib.cityu.edu.hk/record=b2217868
Appears in Collections:AP - Doctor of Philosophy

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