Preparation And Characterization Of Bi_0.5Na_0.5TiO₃Oriented Thin Film And Hybrid-strcutred Particles

Bi_0.5Na_0.5TiO₃（BNT） is widely used in the area of mechanic, electronic and precisecontrol due to its good properties of ferroelectric, a relative large piezoelectric constantand a small dielectric constant. Oriented thin films of high properties are most commonlyprepared by RF magnetron sputtering, metal organic chemical vapor deposition, pulsedlaser deposition, and sol-gel method. These synthesis methods all call for costly equipmentand unique oriented single crystal substrates, which set a limit for the performance of thinfilm.Titania nanosheet is highly2D anisotropy with a thickness of1nm and lateral sizeranging from sub-micrometers to tens of micrometers. It can be used as a template for thesynthesis of axis-oriented titanium-containing compound, high performance catalysts andcarrier for bio-medical materials.In this study, K_0.8Ti_1.73Li_0.27O4（KTLO） was first prepared via solution combustionmethod （SCS） and was subsequently acid-exchanged and exfoliated into titania nanosheet.Then titania nanosheet was used as precusors for the transformation of highly orientedH1.06Ti1.72O4（HTO） thin film into oriented BNT thin film through a hydrothermal reactionroute. Hybrid micro/nano structured BNT particles were also prepared duringhydrothermal reaction.This research focuses on the effects of SCS parameters on the preparation of titaniananosheet and influence of the parameters of hydrothermal reaction on the crystal phasestructure and morphology of the obtained products, like duration time, reaction conditionand temperature. The products are characterized using X-ray diffraction analysis （XRD）,Field-emission scanning electronic micrograph （FESEM）. Different reaction mechanismswere shown. The main results of this study are listed as following: 1) A pure phase of KTLO was obtained at a low temperature （600°C） with a fuel tooxidizer ratio of1.5. As-prepared particles exhibited plate-like shape with alength of30-50μm and a thickness of about10μm. After the as-prepared productwas post solution combustion heat-treated （1100°C for2hours）, the particlesbecame well crystallized. The heat-treated particles decreased to a length of10-30μm and a thickness of about5μm with a smooth surface due to amelting-recrsallization process. Tiania nanosheet can be obtained via acidexchange and exfoliation of prepared KTLO. The prepared nanosheet exhibits alateral size of1-5μm with a thickness of2nm.2) Titania nanosheets were spin-coated onto the Pt substrate to form a highlyanosotropic HTO thin film. A pure phase of （110）-oriented BNT thin film can beobtained within12hours with a reaction temperature exceeding200°C. Theorientation degree of （110） crystal facet exceeds99%. This thin film is composedof densly packed cubic crystal grains. The similarity of crystal structure betweentitania nanosheet and BNT can guide the axis-oriented growth of BNT thin film.3) Hybrid structured particles of BNT were obtained via hydrothermal reaction oftitania nanosheets colloidal suspension at a temerpature of140°C and160°C. Thehybrid structure consists of plate-like HTO particles and hierarchical sphericalBNT particles. The hierarchical spherical BNT particles are assembled by BNTnanosheet. This structure exhibits a high surface area and photocatalytic activity.