Stucture property relations in anion ordered phases

材料化学在很大程度上依赖于结构的可靠测定。晶体材料最好用衍射法研究。粉末衍射方法在过去十年中有了显著的改进，由于高分辨率衍射仪和先进的数据分析工具，现在是可靠的方法，几乎接近单晶衍射实验的性能。使用各种还原性、惰性和氧化性气氛的高温衍射实验现在使我们能够以极好的时间分辨率跟踪固态反应。这些实验将提高我们对固态反应的理解，从而将允许优化固态合成方法。稀土过渡金属氯氧化物和还原稀土过渡金属氧化物是低维磁性亚晶格的模型化合物。利用不同阴离子的各向异性磁交换路径，实现了低维顺磁亚晶格。所研究的体系将具有有序和无序阴离子晶格的混合阴离子（氧氯化物）与单阴离子晶格（氧化物）结合在一起。这些模型系统提供了一个机会来评估阴离子排序对扩展固体中磁交换相互作用的影响。用衍射和差热分析方法研究了晶体学相变。这个研究项目有一个很大的合成部分，结合了物理性质的研究。体的物理性质和结构细节将被联系起来，试图确定结构-性质的关系。

Materials chemistry depends to a large extent on reliable determination of structures. Crystalline materials are best investigated by diffraction methods. Powder diffraction methods have been improved significantly during the last decade and due to high-resolution diffractometers and advanced data analysis tools are now reliable methods, almost approaching the performance of single crystal diffraction experiments. High temperature diffraction experiments using a variety of reducing, inert and oxidizing atmospheres permit us now to follow solid state reactions with excellent time resolution. These experiments will improve our understanding of solid state reactions and thus will permit to optimize solid state synthesis methods. Rare-earth transition metal oxychloride and reduced rare-earth transition metal oxides are targeted as model compounds for low-dimensional magnetic sublattices. Low-dimensional paramagnetic sublattices are being realized by means of anisotropic magnetic exchange paths due to different anions. The systems under investigation combine mixed anions (oxychlorides) having ordered and disordered anion lattices with single anion lattices (oxides). These model systems provide an opportunity to evaluate the impact of anion ordering on magnetic exchange interactions in extended solids. Crystallographic phase transitions are investigated by diffraction and differential thermal analysis methods. The research program has a large synthetic component combined with the investigation of physical properties. Bulk physical properties and structural details will be correlated in an attempt to identify structure - property relations.