Synthesis And Optical And Electrical Properties Of Relaxor Ferroelectric Materials

In recent years, all kinds of electronic products, such as:microelectronics, fluorescent display, optoelectronics and solar cell, which based on informational and functional oxide materials have penetrated into every aspect of our daily life. In particular, the perovskite relaxation ferroelectric materials, wide band gap semiconducting oxide, and rare earth metal oxide doping are the hotspot of current research materials. Especially, relaxor ferroelectrics materials, which are characterized by pyroelectric, ferroelectric/antiferroelectric, electrical piezoelectric, dielectric, electrostrictive, and nonlinear optical properties have recently attracted tremendous attention as a candidate class of materials for use in the fields of optoelectronics, microelectronics, microelectromechanical systems, integrated iron electrical disciplines and devices electro-optic modulators. In order to develop the potential application of perovskite ferroelectric materials, it is necessary to further study the optical and electrical properties. It is important to emphasize that the photoelectric transition which is closely related to electronic band structure, play an important role in Optics Design. By optical spectroscopy measurements, one can further obtain the band gap Eg, optoelectronic transitions, and free carrier behavior of the samples. Meanwhile, to test whether these materials can work under the condition of variable temperature, we may judge the evolution of the optical constants, electronic excitation, and absorption coefficient with temperature. In addition, optical study is not noly can be obtained the optical constant, but also electronic structure for bulks and films. As is well-known, films are expected to yield better sensitivity, faster response, and better integrate characteristics such as silicon than the bulk materials. Therefore, it is necessary to carry out a further study on the optoelectronic transitions of ferroelectric film materials. The main research works and innovations of this dissertation are listed as follows:1. The relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-0.2PbTiO3 (PZN-0.2PT) films have been fabricated on (100) SrTiO3 substrates by the sol-gel method. The optical band gap and internal electronic transitions were studied using ellipsometric spectra with different temperature.The PZN-0.2PT films were prepared by the sol-gel method. The structure, optical properties and electronic transformations have been investigated using X-ray diffraction, atomic force microscopy, scanning electron microscopy and ellipsometric spectra. We obtained the best crystallization temperature being 600℃. The highly a-axis (100)-preferential orientation and low screw dislocation were obtained at 600℃. Moreover, the red-shift trend of the electronic transformations and the evolution of dielectric constant with temperature induced by the electron-phonon interactions and lattice thermal expansion were observed. Interestingly, a distinct difference of optical behavior and structure can be observed at about 500 K, which reveal tetragonal to cubic structural transition of the 0.8PZN-0.2PT films. It indicates that the potential application of ellipsometric spectra in judging the phase transitions and symmetries of ferroelectric material.2. Characterized by X-Ray diffraction, temperature dependent dielectric permittivity and Raman spectra, phase transition was observed for Pb1-xSrx(Al1/3Nb2/3)0.1(Zr0.52Ti0.48)0.9O3(xSr-PAN-PZT) ceramics with increasing Sr concentration. Phase transition undergoes in Sr concentration of 5% and 10%. Phase transition from rhombohedral to tetragonal was obtained in temperature dependent measurements.Rhombohedral phase of xSr-PAN-PZT displays a single diffraction peak locating at～45° for XRD profile, while rhombohedral and tetragonal phases present different doublet peaks at the same diffraction angle. Based on the different doublet peaks for rhombohedral and tetragonal phase, we can compare with the peak intensity for lower diffraction angle and higher diffraction angle to jude each other. If the intensity of the lower diffraction peak is stronger than the higher diffraction peak, which indicate the sample belongs to rhombohedral phase, on the other hand, to tetragonal phase. Thus, the room temperature XRD analysis shows that the phase transition undergos rhombohedral to tetragonal transformation with increasing the Sr concentration. In addition, the broad dielectric peaks present the diffused phase transition from tetragonal to cubic structure shifts to lower temperature with increasing Sr composition. The dramatic changes of frequency and full width at half-maximum (FWHM) for E(TO4)’ softing mode can be observed at morphotropic phase boundary (MPB). Moreover, the MPB characteristic shows a wider and lower trend of temperature region with increasing Sr composition. Based on the aforementioned discussion, the related phase transition and temperature dependent phase transition are obtained from the different XRD profiles, temperature dependent dielectric permittivity and Raman spectra.3. In preliminary combined with the study of Pb-based materials xSr-PAN-PZT ceramics, we further explore the phonon mode, ferroelectric polarization, dielectric, the polarization current, strain, the compressive stress, the change of domain and domain mechanism with the evolution of components for rare earth metal oxide Dy2O3 doped 0.935 (Na1/2Bi1/2)TiO3-0.065BaTiO3 (xDy-NBBT). Also, we try to combine as many as physicochemical properties of xDy-NBBT ceramics to suitable for fabricating actuators.Highly-purity xDy:NBBT ceramics with Dy3+ doping levels of 0%,0.5%,1%; and 2% were synthesized by standard solid-state reaction sintering method. The microstructure, phonon modes, electrical properties, and domain configuration have been systematically discussed..(a) The X-ray diffraction analysis shows that the ceramics are polycrystalline with a pure perovskite structure. With the improvement of Dy3+ doping concentration, several main diffraction peaks of samples such as (111) and (200) move to higher diffraction angle, then, to lower diffraction angle, and conform the phenonmenon observed in Raman spectrum. (2) A transformation from typical ferroelectric structure to "non-ferroelectric" and gaint strain were observed. Regarding the domain switching mechanism, we design a schematic domain switching diagram in terms of the defect symmetry following the polar tetragonal symmetry in each domain. As is well-known,90°and 180° domain can switching under external E-field and accompanying the domain switching generates a large strain. Nevertheless, the 90°domain is unstability states. So the strain can revert to zero when the E-field is back to zero because the defect symmetry and defect dipole moment cannot be rotated by oscillating E-field input. The unswitchable defect dipole moment provides a reverse internal field to facilitate a reverse domain switching as E-field decrease to zero, (c) In order to understand the variation of domain configuration with Dy3+ concentrations, PFM measurement was performed. Comprehensive analysis showed that domain configuration is related to the crystal structure and the relationship between the domain switching with crystal structure of each sample, respectively. (d) The emission of Dy3+ in different Ti4+ lattice sites exhibits blue (4F9/2â†' 6H15/2) and yellow (4F9/2â†'6H13/2) lights. The yellow emission belongs to the hypersensitive transition, intensely affected by the crystal-field environment. Hence, it is possible to obtain white light by adjusting the intensity ratio of yellow to blue for Dy+ -activated single phosphor materials. The experiment showed that the intensity of the emission band becomes stronger with increasing the concentration of Dy3+. However, with temperature increasing, the intensity of the emission band for a same sample become weaken.