| The Aurivillius family of bismuth-containing oxides encompasses many promising materials of potential use in non-volatile ferroelectric random-access memory and high-temperature piezoelectric devices due to their well-known fast switching speed, fatigue-free properties, relatively high Curie point (Tc) and lead-free chemical composition. However, as the spontaneous polarization movements are confined to the a(b) plane, the relatively smaller remanent polarization (2Pr) and lower piezoelectric activity of pure Aurivillius members such as B4Ti3O12 (BIT, 2Pr = 15μC/cm2) and SrBi4Ti4O15 (SBTi, 2Pr = 6.2– 13.0μC/cm2) are not so satisfactory when compared with PZT film in high-density integration of memory cell and pressure sensors applications. The main purposes of this dissertation are aimed at the modification of such Aurivillius phases and, briefly speaking, it can be summarized into following three parts:(1) Effect of Nd modification on ferro-, piezo- and dielectric properties of intergrowth Bi4Ti3O12-SrBi4Ti4O15 ceramics were investigated. X-ray diffraction and Raman scattering were used to identify the crystal phase and to distinguish the doping sites. With increasing Nd content up to 0.50, both remanent polarization (2Pr) and piezoelectric coefficient (d33) were found to increase and reach the maximum value of 33.2μC/cm2 and 14 pC/N, respectively, which gained an enlargement over 1.7 times in 2Pr and a desirable 75% increment in d33 value. However, further Nd modification starts to deteriorate the ferro- and piezoelectric behavior. Impedance spectroscopy shows the activation energy of conductivity increased with increasing Nd content, which can be regarded as direct proof of the restraint of oxygen vacancies. The thermal variations of dielectric permittivity and loss tanδwith Nd content show the characteristic of diffuse phase transformation while the convincible defect-related relaxation phenomenon was not found. Interestingly, in contrast to La modification, Nd modification does not induce the relaxor behavior even at very high doping content.(2) Electrical properties of Nb-, V-, and W-doped Bi4Ti3O12-MBi4Ti4O15 (BIT-MBTi, M = Ca, Sr) compounds were investigated. The remanent polarization (2Pr) and piezoelectric coefficient (d33) of BIT-MBTi are greatly increased by such donor doping. W-doped and Nb-doped BIT-SBTi exhibited the greatest enlargement in 2Pr and d33, respectively. Nb doping also increases 2Pr and d33 of BIT-CBTi though not that much as in BIT-SBTi case. BIT-CBTi thin film shows a high 2Pr value of 39μC/cm2. The enhanced properties are thought to stem from the reduced concentration and weakened mobility of oxygen vacancies. Increased activation energy of conduction further confirmed the restraint of oxygen vacancies. The different optimal V-doping content for 2Pr and d33 in BIT-SBTi might be related to the fact that V-doping could affect the structure and density of domain more apparently than the concentration of oxygen vacancies. The thermal variation of dielectric constant of BIT-CBTi shows a distinctive double anomaly at 658°C and 728°C. The first dielectric anomaly is related to the regulation of BIT parts and the second one corresponds to the ferro-paraelectric phase transition.(3) Thin films of Fe-containing Aurivillius phase Bi5FeTi3O15 (BFTO) were prepared using chemical solution deposition method. The structures of the films were analyzed using x-ray diffraction and Raman spectroscopy. The surface topography and crystal microstructure were characterized by AFM and FESEM. The remanent polarization (2Pr) and coercive field (Ec) of BFTO thin films under an electric field of ~570 kV/cm are determined to be 35.5μC/cm2 and 171 kV/cm, respectively. The normalized polarization of BFTO thin films under 285 kV/cm decreased to 66% after being subjected to 5.2×109 read/write cycles. Comparison between BFTO and SrBi4Ti4O15 in Raman spectra and ferroelectric behavior is also presented. The leakage current density measurement reveals the conduction mechanism of BFTO thin films in the intermediate electric field range from ~50 kV/cm to ~200 kV/cm is dominated by Schottky emission. With electric field higher than ~200 kV/cm, the leakage behavior is mingled with different conduction mechanisms.We have also synthesized Bi5Fe0.5Co0.5Ti3O15 ceramics by a multi-calcination-method. The Aurivillius structure with four-octahedra in between two Bi-O layers is confirmed by the XRD pattern and HRTEM image. The BFCT sample exhibits the coexistence of ferroelectric and ferromagnetic orders above room temperature, with its 2Pr and 2Mr at RT of 13μC/cm2 and 7.8 memu/g, respectively. The magnetic behavior below 275°C is spin-glass type and the Curie temperature is determined at ~ 345°C.
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