【作者】 何万波；

【导师】 徐刚；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2011， 硕士

【摘要】 钙钛矿结构钛酸铅(PbTiO3)作为一种典型的铁电材料,其纳米结构材料的制备引起人们的广泛关注。目前,人们利用熔盐法获得了钙钛矿结构PbTiO3单晶纳米棒,但相对复杂的钙钛矿结构PbTiO3纳米结构的制备仍然是一个挑战。本研究利用水热法,通过选择矿化剂的种类来调控钛酸铅的成核及生长,首次实现了钙钛矿结构PbTiO3纳米片自组装花状纳米结构和烧绿石结构钛酸铅(Pb2T12O6)三维单晶枝杈晶纳米结构的制备。通过将合成的Pb2T12O6枝权晶在高温下进行热处理,制备了钙钛矿结构PbTiO3单晶枝权晶纳米结构。取得的主要研究成果如下：采用钛和铅的羟基氧化物的混合物(PTOH)作为前驱体,12M KOH作为矿化剂,通过水热反应前期形成的单斜相六钛酸钾(K2Ti6O13)的先导性作用,在200℃水热反应50h后,合成出了钙钛矿结构PbTiO3纳米片自组装花状纳米结构。高浓度的矿化剂和足够量的反应前驱体用量是获得PbTiO3纳米片自组装花状纳米结构的关键。在高浓度矿化剂KOH的作用下,水热反应前期首先形成K2Ti6O13纳米线。随后,Pb2+离子逐渐取代K2Ti6O13结构中的K+离子,使得K2Ti6O13纳米线转化为PbTiO3纳米片。随着转化的进行,PbTiO3纳米片自组装形成花状纳米结构。当前驱体用量较少时,Pb2+离子不能够完全取代K2Ti6O13中的K+离子,只有少量的PbTiO3形成,不能得到其花状纳米结构。采用NH3·H2O作为矿化剂,通过控制水热条件下晶体形核和生长缓慢地进行,在200℃水热反应50h后,合成出了烧绿石结构Pb2T12O6的单晶枝权晶纳米结构。矿化剂氨水对Pb2Ti2O6枝权晶的形成具有关键作用。水热反应过程中,在弱碱性的氨水的作用下,形成的钛和铅的离子聚集体的浓度较低,有利于介稳相烧绿石结构Pb2Ti2O6的形核和生长,抑制了钙钛矿结构PbTiO3的形成,又由于所形成的钛酸铅单体具有TiO6八面体通过共顶连接所形成的链状结构,易于沿着Pb2Ti2O6的晶体结构中同样有着这种链状结构的<112>晶向族的24个方向沉积,使得Pb2Ti2O6发生取向生长,从而得到Pb2Ti2O6单晶枝杈晶纳米结构。由于钙钛矿结构PbTiO3和烧绿石结构Pb2Ti2O6的结构骨架都是TiO6八面体共顶连接形成的三维网络,具有拓扑相似性,Pb2Ti2O6单晶枝权晶在600℃热处理2小时后转化为了PbTiO3单晶枝权晶纳米结构。只是由于Ti06八面体网络结构的调整和Pb2+离子的重排,枝权晶的表面变得模糊钝化。更多还原

【Abstract】 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.更多还原