Influences Of Point Defects And （111） Twins On Related Properties Of BaTiO₃Crystallites

BaTiO3has been extensively investigated by researchers from every corner of the world due to its excellent ferroelectric, piezoelectric, dielectric and optical nonlinear properties,. As ferroelectric devices gradually evolve towards miniature and integration, high performance BaTiO3materials are required crucially. The applications of BaTiO3are transforming from single crystal, bulk ceramic to low dimensional structures such as thin film, nanowire and nanoparticle. Along with the reduction of the dimensions, the proportion of defects in materials increases and the effects associated with microstructual defects become more significant. Therefore, it becomes both scientifically and technologically of importance to characterize defects, to understand their formation mechanisms, to study the effects on materials properties, and to control the distribution and concentration in the materials. In this thesis, BaTiO3particles were synthesized and BaTiO3thin films were fabricated. The influence of the point defects and (111) twin on related properties of BaTiO3was investigated. Through doping, the concentration of the (111) twin in BaTiO3particles was changed. The influence of the doping defects on the morphology of BaTiO3thin films was analyzed.BaTiO3microcrystallites were synthesized by using Ti2O3powders as the raw material through a modified hydrothermal method. The BaTiO3contains abundant (111) twinned microcrystallites, along with a large amount of oxygen vacancies and Ti3+cations. The formation mechanism of (111) twin was analyzed and discussed in this thesis. Due to the unique structure, these BaTiO3particles exhibit interesting reversible photochromic effects. The color of these particles can change from pale yellow to reddish brown under ultraviolet light and change back with the illumination of infrared light or by thermal treatment. In addition, these BaTiO3particles present lower phase transition temperature than normal BaTiO3. All these changes are attributed to the presence of the large number of defects (such as Ti3+ions and oxygen vacancies) in the material. BaTiO3nanoparticles synthesized under high Ba/Ti ratio also show the photochromic effect with the irradiation of lasers of different wavelengths. This is also the results of the impact of defects including Ti vacancies and oxygen vacancies on the material property.In addition, the BaTiO3particles were doped with different elements through the modified hydrothermal method. As the doping elements can influence the nucleation and growth of BaTiO3particles, the concentration of (111) twin was changed throuth doping. The doping of elements that replace positions of Ti in BaTiO3can make the interpenetration of the (111) twinned particles much denser. And, with the increase of Ba/Ti ratio, the solubility limit of the doping elements rises, the amount of the (111) twinned particles becomes higher. La can only substitute Ba once doped into BaTiO3. The as-synthesized La-doped BaTiO3particles are cubes with size ranging from80nm to200nm and seldom (111) twinned structure appears.The doping of BaTiO3thin films results in the changes of morphology and size of the particles that make up the thin films. In addition, BaTiO3single crystal was etched and etching hillocks were formed when air bubbles or TiO2attached on the surface of the single crystal during the etching process under UV irradiation.Through controlling the growth condition and doping different elements, point defects and (111) twin was controlled, and thus related properties of BaTiO3particles including photochromic properties and dielectric properties were changed.. These are very helpful to understand the influence of defects on the BaTiO3properties and applications.