Study On The Preparation And Growth Mechanism Of Lead Titanate Nanostructures

As a kind of prototypical ferroelectric material, the preparation of perovskite lead titanate(PbTiO3) nanostructured materials has attracted great attention. Up to now, the single crystal nanorods of PbTiO3 have been synthesized successfully through a molten salt method. However, the synthesis of complex PbTiO3 nanostructures still remains a challenge. In the thesis, by using different kinds of mineralizers to control the nucleation and growth, perovskite PbTiO3 flower-like nanostructures assembled by nanosheets and single crystal pyrochlore Pb2Ti2O63-dimensional dendrites have been successfully hydrothermal synthesized for the first time. By calcining the prepared Pb2Ti2O6 dendrites, single crystal perovskite PbTiO3 dendrites have been successfully fabricated. The main results include:By employing the as-prepared mixture of lead and titanium hydroxides as precursors, and 12M potassium hydroxide(KOH) as mineralizer, perovskite PbTiO3 flower-like nanostructures assembled by nanosheets have been synthesized via a hydrothermal treatment at 200℃for 50h. The high concentration of mineralizer and enough amounts of precursors play key roles in the formation of PbTiO3 flower-like nanostructures. In the initial stage of the hydrothermal reaction, monoclinic K2Ti6O3 nanowires preferentially form under the effect of KOH with high concentration. Subsequently, with the extension of hydrothermal reaction time, Pb2+ions penetrate into the crystal lattice of K2Ti6O13 and exchange with K+ions, which drives K2Ti6O13 nanowires to transform to PbTiO3 nanosheets. With the transformation proceeding, these nanosheeets assemble into PbTiO3 flower-like nanostructures. When limited amount of precursors was used, only a few K+ions are exchanged with Pb2+ions, hindering the formation of PbTiO3 flower-like nanostructures.Single crystal pyrochlore Pb2Ti2O6 dendrites have been synthesized via a hydrothermal treatment at 200℃for 50h by employing ammonia (NH3-H2O) as mineralizer to control the nucleation and growth to occur slowly. The mineralizer NH3-H2O plays a key role in the formation of Pb2Ti2O6 dendrites. During hydrothermal treatment, the finite amounts of lead titante monomers occurring under the effect of alkalescent NH3-H2O favors the nucleation and growth of pyrochlore Pb2Ti2O6, and suppresses the formation of perovskite PbTiO3. The formed lead titante monomers, which are of corner-sharing TiO6 octahedrons chain-structure, prefer to attach along<112>, resulting in the oriented growth of Pb2Ti2O6 nuclei along these directions and finally realizing Pb2Ti2O6 dendrites.By calcining the pre-obtained pyrochlore Pb2Ti2O6 dendrites at 600℃for 2h, the single crystal PbTiO3 perovskite dendrites have been fabricated because pyrochlore structure has a topologically equivalent network of corner-sharing TiO6 octahedrons as the framework to perovskite structure. However, since the adjustment of the framework and rearrangement of Pb2+ions, the facets of the obtained single crystal PbTiO3 perovskite dendrites become blurry.