Effects of compensating doping or chemical pressure in 122-type superconductors and structure-property relations of superconducting platinum-iron arsenides with layered structures

在这个项目中，我们正在研究砷化铁超导体的细微晶格效应和晶体化学。我们期望在电子自由度和晶格自由度的相互作用方面有新的见解，并扩大砷化铁的物质基础。这些最近发现的材料代表了继铜酸盐之后的一类新的高tc超导体。超导性发生在FeAs层中，由充当电荷储层的间隔层隔开。目前的材料基础由三种已知的结构类型组成，它们具有相似的FeAs层，但不同的分离层。人们普遍认为，砷化铁的超导性是非常规的，但晶格在配对机制中的作用还远远不清楚。在第一次发现靠近Tc的LaFeAsO晶格异常后，我们将利用高分辨率单晶x射线衍射来寻找与传统三维晶体结构的偏差。通过充分利用这种方法的能力，我们将获得关于非调和原子位移、调制或超晶格的详细信息。我们还将绘制CaFe2As2的实验电子密度图。该项目的第二个分支致力于通过增加这些材料的各向异性来增加它们的Tc。我们将探索和表征具有大分离块的FeAs化合物，如Sr2VO3FeAs (Tc = 37 K)，并寻找含有非等效FeAs层的多层结构。这些材料将通过x射线和中子衍射、磁测量和Mössbauer光谱学进行研究。

In this project we are studying subtle lattice effects and the crystal chemistry of iron arsenide superconductors. We expect new insights in the interplay of electronic and lattice degrees of freedom as well as a widening of the material basis of iron arsenides. These recently discovered materials represent a new class of high-Tc superconductors after the cuprates. Superconductivity takes place in FeAs layers, separated by spacers acting as charge reservoirs. The current material basis consists of three well known structures types with similar FeAs layers, but different separating layers. It is generally accepted, that superconductivity is unconventional in iron arsenides, but the role of the lattice for the pairing mechanism is far from being clear. Following a first hint at lattice anomalies in LaFeAsO close to Tc, we will search for deviations from the conventional three-dimensional crystal structure by using high resolution single crystal X-ray diffraction. By exploiting the full capacity of this method, we will obtain detailed information about anharmonic atomic displacements, modulations, or superlattices. We will also map the experimental electron density of CaFe2As2. The second branch of the project is devoted to increase the Tc of these materials by increasing their anisotropy. We will explore and characterize FeAs compounds with big separating blocks like Sr2VO3FeAs (Tc = 37 K) and also search for multilayer-structures containing non-equivalent FeAs layers. The materials will be studied by X-ray and neutron diffraction, magnetic measurements and Mössbauer spectroscopy.