Determining the atomic structure of incommensurate antiferroelectrics based on La-doped Pb(Zr,Ti)O3

基于 La 掺杂 Pb(Zr,Ti)O3 的不相称反铁电体的原子结构测定

• 批准号: EP/H028218/1
• 负责人: Ian MacLaren
• 金额: $ 0.48万
• 依托单位: University of Glasgow
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH028218%2F1
• 关键词: Determining; atomic; structure; incommensurate; antiferroelectrics

The lead zirconate titanate (Pb(Zr,Ti)O3) system displays a fascinating range of structures and behaviours, but with the common feature that all compositions contain exhibit permanent electric polarisation at room temperature as a result of antiparallel displacements of the oxygen anions and the metal cations. At the PbZrO3 end of the composition range, the electric dipoles are arranged in stripes of antiparallel polarisation resulting in zero net polarisation, this is referred to as an antiferroelectric state. In contrast to this, for Pb(Zr[0.9],Ti[0.1])O3, polarisation all lies along the same direction resulting in a finite permanent macroscopic polarisation - a ferroelectric state. Just doping this latter composition with 2-4% La puts this into a slightly confused state, very much on the edge between ferroelectric and antiferroelectric ordering. Whilst it is well known that the crystal structure for this state has a large unit cell, which is incommensurate (i.e. it doesn't quite stack up as being made of a simple whole number of atomic stackings), the details of this structure are not at all well understood. The reasons for this are straightforward: it is big and not perfectly ordered (previous studies show frequent deviations from perfect order) and thus techniques like diffraction with X-rays or neutrons will have difficulties. Whilst some information can be inferred from conventional electron microscopy and diffraction (which has already been done by the applicant), the most straightforward way to solve the structure would be to be able to see where all the atoms are. This is now possible due to advances in aberration corrected electron microscopy. Recent developments have made it possible to compensate for the imperfections present in all electromagnetic lenses and this now allows us to resolve objects well below 1 + - a suitable scale for resolving atoms. The project partners at Jlich are world leaders in applying this to materials and have particular experience with doing such studies on perovskite oxides and in measuring electrical polarisation from imaging the oxygen and the metal cations in these structures. This project will allow the applicant with his prior experience of incommensurate antiferroelectrics to travel to Jlich and collaborate with them on imaging these fascinating materials at sub-+ngstrm resolution and in combination with data processing and image simulation to enable us to be able to determine the oxygen and cation displacements across the unit cell. As well as solving the structure of this interesting phase, it will also enable us to better understand its relationship to both the ideal antiferroelectric phase of PbZrO3 and to the rhombohedral ferroelectric phase of Pb(Zr[0.9],Ti[0.1])O3, and will prepare the ground for future studies of field induced transformations between antiferroelectric and ferroelectric phases.

锆钛酸铅（Pb(Zr,Ti)O3）体系表现出一系列令人着迷的结构和行为，但其共同特征是，由于氧阴离子和金属阳离子的反平行位移，所有成分都在室温下表现出永久的电极化。在组成范围的PbZrO3端，电偶极子排列成反平行极化条纹，导致净极化为零，这被称为反铁电态。与此相反，对于Pb(Zr[0.9],Ti[0.1])O3，极化都沿着同一方向，导致有限的永久宏观极化-铁电态。仅仅在后一种组合物中掺杂2-4%的镧，就会使其处于一种稍微混乱的状态，处于铁电有序和反铁电有序的边缘。虽然众所周知，这种状态的晶体结构有一个大的单晶胞，这是不相称的（即它不完全堆叠，因为它是由简单的原子堆叠组成的），但这种结构的细节还没有得到很好的理解。原因很简单：它很大，而且不是完全有序的（以前的研究表明经常偏离完美的有序），因此像x射线或中子衍射这样的技术将会有困难。虽然一些信息可以从传统的电子显微镜和衍射中推断出来（这已经由申请人完成），但解决结构的最直接方法是能够看到所有原子的位置。由于像差校正电子显微镜的进步，现在这是可能的。最近的发展使得补偿所有电磁透镜中存在的缺陷成为可能，这现在使我们能够分辨远低于1 +的物体——一个适合分辨原子的尺度。Jlich的项目合作伙伴在将其应用于材料方面处于世界领先地位，并且在钙钛矿氧化物的研究以及通过对这些结构中的氧和金属阳离子成像来测量电极化方面具有特别的经验。该项目将允许申请人带着他之前对不匹配反铁电体的经验前往Jlich，并与他们合作，以亚+ngstrm分辨率对这些迷人的材料进行成像，并结合数据处理和图像模拟，使我们能够确定整个单元胞中的氧和阳离子位移。除了解决这个有趣的相的结构，它还将使我们更好地理解它与PbZrO3的理想反铁电相和Pb(Zr[0.9],Ti[0.1])O3的菱形铁电相的关系，并将为未来研究反铁电相和铁电相之间的场诱导转化奠定基础。