Ordered States in Oxides

过渡金属氧化物的电子性质继续推动许多领域，从基础凝聚态物理和固态化学到材料科学和工程应用。铜氧化物的高温超导性（HTSC）和钙钛矿锰氧化物的巨磁阻（CMR）是两个特别重要的现象，这使得许多其他钙钛矿氧化物的电子性质得到了广泛的研究。结构知识对于理解材料性质总是很重要的。过渡金属氧化物结构通常基于简单的高对称性结构，例如钙钛矿、尖晶石，但上述排序降低了对称性，导致轻微的晶格畸变和超结构。很明显，可以从高分辨率粉末衍射研究中获得许多微妙但重要的信息。需要粉末衍射的部分原因是这些材料中的许多难以结晶，但更根本的是，扭曲导致晶体中严重的（微）孪生，这使得传统的单晶结构测定变得困难（例如在Fe3O4的情况下）。粉末衍射是一种简单的技术，但仍然是同步加速器X射线和中子用户社区中最流行的技术之一。现在ISIS、ILL、ESRF和（将来）Diamond都有各种各样的仪器。这些应用于化学，物理，材料科学，工程和地球科学中的许多问题。为了充分利用现有的设备，以及提供领先的粉末衍射技术的广泛培训，本项目将使用一系列仪器研究几种材料。将研究高压Cr，Ru和Bi基钙钛矿的结构和磁序。这些材料将使用最近委托的步行者新闻合成。RBaMn_2O_6锰氧化物中与电荷、自旋和轨道序相关的复杂超结构也将被研究。磁铁矿（Fe_3O_4）中的电荷有序是一个经典的、长期存在的问题。我们的目标是通过进一步的高分辨率粉末衍射研究，并从大量孪生微晶分析数据，以改善以前的结构模型。学生培训的其他方面将通过参加格勒诺布尔（HERCULES）和ISIS的研讨会，以及对每个中心进行为期3个月的访问。

The electronic properties of transition metal oxides continue to drive many fields, from fundamental condensed matter physics and solid state chemistry to materials science and engineering applications. High temperature superconductivity (HTSC) in copper oxides and colossal magnetoresistances (CMR) in manganite perovskites are two particularly important phenomena that have led to many other perovskite oxides being widely studied for their electronic properties.Knowledge of structure is always important for understanding materials properties. Transition metal oxide structures are often based on simple high symmetry structures e.g. perovskite, spinel, but the above orderings lower symmetry leading to slight lattice distortions and superstructures. It has become clear that much subtle but important information can be gained from high resolution powder diffraction studies. Powder diffraction is needed partly because many of these materials are difficult to crystallise, but more fundamentally, the distortions lead to severe (micro)twinning in crystals that makes conventional single crystal structure determinations difficult (e.g. in the case of Fe3O4).Powder diffraction is a simple technique but remains one of the most popular in the synchrotron X-ray and neutron user communities. A variety of instruments are now available at ISIS, ILL, ESRF and (in the future) Diamond. These are applied to many problems in chemistry, physics, materials science, engineering and geosciences. To make the best use of available facilities, as well as providing a broad training in leading powder diffraction techniques, this project will study several materials using a range of instruments.The structures and magnetic order in high pressure Cr, Ru and Bi-based perovskites will be investigated. These materials will be synthesised using a recently commissioned Walker press. The complex superstructures associated with charge, spin and orbital order in RBaMn2O6 manganites will also be studied. Charge ordering in magnetite (Fe3O4) is a classic and long running problem. We aim to improve on a previous structural model through further high resolution powder diffraction study, and analysing data from heavily twinned microcrystals. Further aspects of the student training will be through attending workshops in Grenoble (HERCULES) and ISIS, and by 3 month visits to each centre.