In order to investigate the structures and physical properties of intriguing relaxor ferroelectrics, a novel solid solution, (1-x)(Pb0.5Sr0.5)(Zr0.5Ti0.5)O3-xPbTiO3 (PSZT-PT), of complex perovskite structure was synthesized by solid-state reaction method. The ceramics of the PSZT-PT system were characterized by X-ray diffraction (XRD), dielectric spectroscopy, ferroelectric testing and transmission electron microscopy (TEM). Detailed structural analyses based on the refinements of XRD patterns by both the Pawley and Rietveld methods reveal a structural transformation from the cubic to tetragonal symmetry as the concentration of PT (x) increases, with a mixture of the two phases in the composition range of x ≈ 0.10 ~ 0.25. Subsequently, the dielectric properties of the PSZT-PT solid solution were characterized as a function of temperature at various frequencies (10 Hz to 1 MHz). The results indicate a crossover from typical relaxor behaviour to normal ferroelectric state with increasing concentration of PT. The characteristics of relaxor behaviour and its evolution were analyzed by the Vogel-Fulcher law and Curie-Weiss law in terms of the dielectric peak temperature (Tmax) shift with frequency, the freezing temperature (Tf) and the Burns temperature (TB). Furthermore, the measurements of polarization versus electric field demonstrate that, as the concentration of PT increases, the ferroelectric hysteresis loop of the PSZT-PT solid solution transforms from a narrow curve to a wide-open loop with enhanced remanent polarization and coercive field, confirming the relaxor to ferroelectric transformation. The domain structures of PSZT-PT were imaged and analyzed by means of TEM. The results show the presence of polar nano-domains in the relaxor composition, which transform into microscopic domains in the ferroelectric compound, revealing the transformation from the relaxor to ferroelectric state on the nano- to micro-scale. The mechanism of the crossover was illustrated from the effects of the substitution of ferroelectrically active lead titanate. Finally, the evolutions of the crystal structures and physical properties of the PSZT - PT solid solution are presented in the forms of structural and dielectric phase diagrams, providing a clear picture of the crossover from relaxor to ferroelectric state in this pseudo-binary system, and the phase diagram of the PbZrO3 - PbTiO3 - SrTiO3 ternary system is established.
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Thesis advisor: Ye, Zuo-Guang
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