Superconducting iron-selenide layered systems by hydrothermal syntheses

超导体在高临界温度（Tc）下具有无与伦比的电子和磁性能，在当前新兴能源技术中具有巨大的应用前景——前提是找到合适的材料。铁基材料最近证明了其固有的优势，超越了众所周知的氧化铜，只是它们的临界温度仍然低于77 K的里程碑。一种具有更高临界温度的新型铁基超导体将是技术适用性的突破。最近在氧化物衬底上生长的极薄硒化铁（FeSe）薄膜中发现了高达99 K的超导性。我们相信这在散装材料中也是可能的。我们项目的目标是创造新的基于FeSe的超导体，其中硒化铁层夹在金属氧化物层或有机分子层之间。我们进一步开发了一种合成方法，其中起始材料在高达200度的高压和温度下的溶剂中反应到所需的化合物（溶剂热合成）。在第一个资助期内，我们成功地生长出了铁磁超导体Li0.8Fe0.2OHFeSe的大单晶。现在我们想用这种晶体进行中子散射实验，以便在超导研究中首次探测到经常被预测的自发涡晶格。此外，我们将溶剂热和离子交换方法结合起来寻找新的插层fes超导体。此外，我们将使用声化学（超声为基础）的方法插入有机分子在硒化铁前体。在第一个资助期，我们已经合成了这样一种混合材料。新化合物FeSe(C2N2H8)0.3被称为“扩展FeSe”，它首次包含了几乎孤立的FeSe层。这将使我们能够弄清楚电子掺杂对于FeSe中的超导性是否本质上是必要的。我们的项目为基于fese的层状超导体的存在、结构和性质提供了新的见解。我们认为这些材料是氧化物衬底上的FeSe薄膜的大块类似物。在这个非常活跃的研究领域，达到77k的里程碑将是一个巨大的突破。

The unrivalled electronic and magnetic properties of superconductors with high critical temperatures (Tc) provide immense application prospects in current end emerging energy technologies - on the condition that suitable materials become available. Iron-based materials have recently demonstrated inherent advantages over the long known copper-oxides, solely their critical temperatures are still below the landmark of 77 K. A new iron-based superconductor with higher critical temperatures would be a breakthrough towards technological applicability. Recently superconductivity up to 99 K was discovered in extremely thin films of iron selenide (FeSe) grown on oxide substrates. We believe that this is also possible in bulk materials. The goal of our project is creating new FeSe based superconductors where iron selenide layers are sandwiched between layers of metal oxide or organic molecules. We develop further a synthesis method where starting materials react in solvents under high pressure and temperatures up to 200 degrees to the desired compounds (Solvothermal synthesis). During the first funding period, we succeeded in growing large single crystals of the ferromagnetic superconductor Li0.8Fe0.2OHFeSe. Now we want to use such crystals for neutron scattering experiments in order to detect the often-predicted spontaneous vortices lattice for the first time in superconductivity research. Furthermore, we combine solvothermal with ion exchange methods in the search for new intercalated FeSe-based superconductors. Additionally we will use sonochemical (ultrasonic-based) methods to intercalate organic molecules in iron selenide precursors. In the first funding period, we have already synthesized such a hybride material. The new compound FeSe(C2N2H8)0.3 is referred to as “expanded FeSe” and contains, for the first time, virtually isolated FeSe layers. This will allow us to figure out whether electron doping is intrinsically necessary for superconductivity in FeSe or not. Our project provides new insights about the existence, structures and properties of FeSe-based layered superconductors. We consider these materials as bulk analogs to the FeSe thin films on oxide substrates. Reaching the 77 K landmark in a FeSe-based bulk superconductor would be a big breakthrough in this very active research field.