| ABO3 type perovskite oxides exhibit many excellent physical properties, such as ferroelectric property, dielectric property, electro-optical effect, pyroelectric property, giant pizeoelectric property and magnetoelectric coupling effect. These excellent properties are essential to its potential application in actuators, sensors, and micro-electromechanical systems (MEMS).Pb(Zr1-xTix)O3 is a typical material of ABO3 type perovskite oxides. Due to its outstanding pizeoelectric property, pyroelectric property and ferroelectric property, it has been widely studied for many years. But there are still some ambiguous problems about its phase diagram and phase structure. The most important one is that the real phase structure of PZT in the vicinity of morphotropic phase boundary (MPB) is still in controversy. In addition, the lattice constants of monoclinic phase (M phase) quite differ in the various literatures. Therefore, clearly demonstrating M phase existence region and dispersion of M phase lattice constant possess a guidance significance for better understanding of PZT phase transition behavior. Residual stress and texture, which are intrinsic properties of thin film material, can greatly affect PZT phase transition behavior and lattice constants. In view of this, thin film material provides a platform for PZT phase transition research.In this dissertation, PZT thin films with the composition nearby MPB have been prepared by sol-gel technology. The residual stress is changed via adjusting film thickness. XRDω-scan andψ-scan are emploied to characterize the texture and residual stress. Based on XRDψ-scan technology, a method is built to characterize the phase compositon of thin film with texture. The dependence of PZT phase transition on the texture and residual stress of thin film is studied in detail. The results show that PZT films with different composition entirely exhibit mixed textures of (100) and (111). Furthermore, the residual stress of (111)-oriented grains is compressive resulting from the lattice mismatch between PZT thin films and Pt substrate, and the residual stress of (100)-oriented grains is tensile due to the stress balance among different oriented grains. The research of phase transition of PZT thin films reveals the phase composition discrepancy of different oriented grains. For Pb(Zr0.58Ti0.42)O3, Pb(Zr0.55Ti0.45)O3 and Pb(Zr0.54Ti0.46)O3 thin films, the phase composition of (100)-oriented grains is MA phase, and that of (111)-oriented grains is MB phase. As the film thickens, the M phase lattice constant ratio of c/a in pseudo cubic approaches 1 gradually, indicating the spontaneous polarization rotation of M phase. For Pb(Zr0.52Ti0.48)O3 and Pb(Zr0.51Ti0.49)O3 thin films with the thickness less than 200nm, the phase composition of (100)-oriented grains is MA phase. However, when the film thickness is more than 200nm, the phase composition of (100)-oriented grains is combined with MA phase and tetragonal phase (T phase), and the content of T phase increases gradually as the film thickens. The phase composition of (111)-oriented grains is the mixture of MB phase and rhombohedral phase (R phase). Moreover, the content of R phase increases gradually as the film thickens. The difference of phase composition between (100)- and (111)-oriented grains can be attributed to the different state of residual stress in different oriented grains. As the film thickens, the residual stress decreases, leading to the spontaneous polarization rotation of M phase, illustrating that the lattice constants of M phase is very sensitive to the variation of residual stress.BiFeO3 (BFO), another typical material of ABO3 type perovskite family, is the only multiferroic material with ferroelectric property and antiferromagnetic property at room temperature. In addition, it had been reported that epitaxial BFO thin film possesses giant spontaneous polarization and piezoelectric property. Unfortunately, the high crystallization temperature and large leakage current restrict its application in the field of function device. Seed layer is a very effective route to decrease the crystallization temperature and leakage current, and can also induce the formation of the film texture. In this dissertation, Bi2O3 as the seed layer was prepared through sol-gel technology. The results show that the BFO thin film without seed layer fails to be crystallized well even at the high annealing temperature of 650oC and exhibites no texture, but the BFO thin film with seed layer can be crystallized well at such a low temperature of 500oC and exhibites the mixed textures.When the external electric field is of 100kV/cm, the leakage current of BFO thin film falls by two orders of magnitude because of the presence of the Bi2O3 seed layer. Taking the above results into consideration, the Bi2O3 seed layer can induce the formation of film texture. Moreover, it can effectively decrease the crystallization temperature and leakage current of BFO thin film.The detailed explanation is as follows. The Bi2O3 seed layer can provide much more nucleation sites for BFO thin film at lower temperature. Therefore, the BFO thin film can be crystallized at relative low temperature. In addition, the Bi2O3 seed layer forms an interface layer between thin film and substrate. In this case, the seed layer decreases the leakage current and enhances the dielectric property of BFO thin film. |
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