The Controllable Synthesis And Characterization Of BaTiO₃ Nanostructures

As a typical perovskite structured oxide, BaTiO3 has found wide applications in microelectronic devices because of its excellent dielectric, piezoelectric and ferroelectric properties. In this thesis, properties, classification and preparation of nanomaterials were firstly reviewed, and then crystal structure, properties and applications of BaTiO3 was summarized. Furthermore, synthesis methods, characterization and property investigations of BaTiO3 nanopowders have been documented.Using KOH as mineralizer, phase formation and morphology development of BaTiO3 nanopowders were studied under hydrothermal conditions.Polymer surfactants were introduced into the hydrothermal system to suppress quick crystal growing for improved dispersion of nanopowders. Hexapod BaTiO3 nanocrystals have been synthesized for the first time using K2Ti6O13 nanowires as precursors, and the formation mechanism of the hexapod nanocrystals were discussed. The main results and conclusions of this thesis are summarized as following:(1) Cubic perovskite phase BaTiO3 nanopowders were prepared hydrothermally. and the effect of reaction time, temperature and KOH concentration on the structure, size and morphology of the powders was also investigated. When the temperature increases from 200℃to 220℃. the size of as-prepared BaTiO3 nanoparticles decreases from 250nm to 100nm. Well-crystallized and dispersed BaTiO3 nanopowders with 100nm in size and uniform morphology have been obtained by a hydrothermal reaction of 48h at 200℃, where Ba/Ti ratio is 1 and KOH concentration is 2mol/L.(2) Polymer surfactants such as PVA and PEG were introduced into the hydrothermal system, and the effect of the surfactants on the size, morphology and dispersion of BaTiO3 nanopowders were discussed. The results indicate the dispersion of the samples has been effectively improved when the surfactants were used. The averge size of BaTiO3 nanoparticles decreases from 150nm to 80nm.(3) Single-crystal hexapod nanostructures of BaTiO3 have been prepared for the first time by a hydrothermal reaction of 24h at 200℃using K2Ti6O13 nanowires as precursors, where Ba/Ti ratio is 1. HRTEM analysis confirms the single-crystal character of hexapod nanostructures, growing along six equaled [100] of the cubic perovskite BaTiO3. The concentration of TiO6 octahedron was low owing to particular crystal structure of K2Ti6O13 considering dissolution-precipitation process under hydrothermal reaction. This manifests the slight difference of surface energy between (100) and (110) of cubic perovskite BaTiO3. favoring intrinsically selectively crystal growth. Hence, the nucleates tend to precipitate on the surface of lower energy (100) and grow into hexapod nanostructures of BaTiO3.(4) Using K2Ti6O13 nano wires as precursors is particularly desirable to control the concentration of TiO6 octahedron during reaction process and then tailors the nucleating-growth dynamics of nanocrytals. This offers a new conception to preparing anisotropic nanostructures of ABO3 perovskite oxides.