Bi4Ti3O12基Aurivillius化合物设计、结构调控和性能研究

Aurivillius compounds are a kind of layered Bi-containing perovskite-related oxides. Its unique layered structure makes the compounds exhibit a variety of excellent physical and chemical properties. However, to date the composition-structure-property relation of Aurivillius compounds is not well understood. That restricts the property-improving and exploiting of Aurivillius compounds. Systematically experimental research on the composition-structure-property relation of Aurivillius compounds is required. The mismatch between (Bi2O2) slab and (An-1BnO3n+1) slab and the tolerance factor of perovskite unit cell, which are two criteria of structural stability of Aurivillius compounds, will be adjusted through element substitution of La, Nd, Ca, Sr, Ba for Bi and Al, Ga, Fe, Co, Nb, Ta, Mo, W for Ti. The effect of ionic size and electronegativity on the ionic distribution, structural distortion and order-disorder transition of the Aurivillius compounds will be studied to verify the key factor which affects the structural stability of Aurivillius compounds and reveal the alloying mechanism. The ferroelectric, dielectric, magnetic and photocatalysis properties will be investigated, together with the structural analysis, to construct the composition-structure-property relation. Mixed-layer Aurivillius compounds will also be designed and prepared since the anticipated unique properties of this kind of compounds and little knowledge of the detailed structure. The structural investigation will concentrate on the mismatches between two perovskite slabs and between the perovskite slabs and the (Bi2O2) slab to find out the key factor in the structural stability of mixed-layer Aurivillius compounds. The project will contribute both theoretical foundation and experimental experience to the material design and the exploiting of novel Aurivillius compounds.

Aurivillius化合物是一类层状钙钛矿衍生结构氧化物，具有诸多优异的物化性能和广阔应用前景。Aurivillius化合物的性能与其独特的层状结构直接相关，但关于这类化合物成分─结构─性能关系的研究还较欠缺，制约了其性能调控和新型化合物的开发。本课题以Bi4Ti3O12为研究对象，采用A位、B位和A/B位离子复合替代，研究替代离子尺寸效应和电负性对离子占位分布、结构畸变和有序-无序转变等结构变化的影响规律，揭示影响结构稳定性的主要因素，结合铁电、介电和光催化等性能表征，建立Aurivillius化合物成分─结构─性能关系。设计和制备新型混合层状结构Aurivillius化合物，研究化合物结构中两种钙钛矿结构单元间及其与(Bi2O2)层间的匹配关系，揭示影响化合物结构稳定性的关键因素和成相规律。项目研究将为新型Aurivillius化合物的设计与开发奠定理论和实验基础。

根据项目研究计划，以Bi4Ti3O12为研究对象，B位采用Fe/Nb/Ta离子替代，A位采用稀土离子（La、Nd、Sm和Gd）、碱金属和碱土金属（Na、K、Sr、Ca和Ba）离子替代/掺杂，制备了不同成分和混合层化合物陶瓷，系统研究了A、B和A/B 位复合替代和掺杂对化合物的晶体结构、铁电转变温度、介电和磁性的影响；采用氩气退火研究了材料高温漏电机制；制备了Bi5Ti3FeO15/BiOCl纳米片异质结和复合薄膜及TiO2/BaTiO3核壳纳米管阵列，研究了铁电复合对材料光催化性能的影响及其机制。研究发现，Bi4Bin-3Ti3Fen-3O3n+3系列化合物当n=>6时，以及4/5层混合层化合物中，存在明显的结构和成分不均匀；B位大尺寸离子替代导致的晶格畸变，不但增强铁电畸变也引入晶格应变能，在奇数层化合物中引起的晶格稳定性降低比偶数层化合物更显著，导致奇/偶层Bi4Ti3O12基化合物表现出不同的Tc变化趋势；Nb和Ta离子能够抑制材料漏电损耗；A位RE离子替代减小了化合物的铁电畸变，但随离子尺寸减小，稀土离子弱化铁电畸变的作用降低，其Tc变化趋势基本符合容忍因子与Tc的关系；随RE离子尺寸减小，对漏电损耗的抑制作用降低；Na/Gd复合替代的Bi4Na0.5Gd0.5Ti4O15陶瓷高温导电激活能高达1.51eV，电导率比Bi4Ti3O12降低了2个多数量级，具有较好的高温压电和铁电材料的应用潜力；Sr掺杂Bi4Ti3O12会诱导电价补偿氧空位生成，降低陶瓷晶内电阻和高温晶界电阻，但通过电荷补偿作用可以抑制材料低温晶界电导；3/4层混合层化合物Bi9Ti6FeO27和Bi8LaTi6FeO27表现出优异的低漏电和高铁电极化率特性，证明混合层状化合物是改善Aurivillius化合物应用性能的有效途径；采用Ar气退火证明了氧空位离子迁移是导致材料高温电导和弛豫行为的主要因素；Bi5Ti3FeO15/BiOCl纳米片异质结可见光降解RhB的效率远高于单相材料和P25，其极化复合薄膜的光电化学研究证明了铁电极化内建电场可以促进载流子分离，导致高可见光催化活性；TiO2/BaTiO3纳米管的光电流密度和光转化效率是纯TiO2纳米管的2倍和2.7倍，光电化学实验证明核壳结构明显提高了光生载流子分离效率，是导致复合材料高光催化活性的主要原因。