Superconducting iron-selenide layered systems by hydrothermal syntheses

具有高临界温度(TC)的超导体无与伦比的电磁性能为当前新兴能源技术提供了巨大的应用前景--只要有合适的材料可用。铁基材料最近显示出了比已知的铜氧化物更多的固有优势，只是它们的临界温度仍然低于77K的里程碑。具有更高临界温度的新的铁基超导体将是技术应用的突破。最近，在氧化物衬底上生长的极薄的硒化铁(FeSe)薄膜中发现了高达99K的超导电性。我们认为，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，其中亚硒化铁被夹在金属氧化物或有机分子层之间。我们进一步开发了一种合成方法，即起始材料在高压和高达200度的温度下在溶剂中反应得到所需的化合物(溶剂热合成)。在第一个资助期间，我们成功地生长了铁磁超导体Li0.8Fe0.2OHFeSe的大单晶。现在，我们希望将这种晶体用于中子散射实验，以便在超导研究中首次探测到经常被预测的自发涡旋晶格。此外，我们将溶剂热方法和离子交换方法结合起来，寻找新的FeSe基插层超导体。此外，我们还将使用声化学(基于超声波)的方法将有机分子嵌入到硒化铁前驱体中。在第一个资助期，我们已经合成了这样的杂化材料。新化合物FeSe(C2N2H8)0.3被称为“扩展FeSe”，并且首次包含虚拟隔离的FeSe层。这将使我们能够弄清楚电子掺杂是否是FeSe超导电性的内在必要条件。我们的项目为研究FeSe基层状超导体的存在、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薄膜的整体类似物。在这个非常活跃的研究领域，达到77K的FeSe基块状超导体将是一个重大突破。

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.