钯铁砷化物Ca10（Fe1-xPdxAs）~（10）Pd_3As_8的超导电性和晶体结构
Superconductivity and Crystal Structure of the Palladium-Iron-Arsenides Ca10(Fe1-xPdxAs)10Pd3As8
摘要：
采用固相法合成了Pd_3As_（10）（Fe_（1-x）Pd_xAs）_（10）（Pd_3As_（8））。三斜晶系的晶体结构（空间群P-1）与具有交替的FeAs 4/4-和Pd 3As 8-层的同系物铂1038型超导体是同型的，每个层由钙原子层隔开。铁是四面体的，钯是由四个砷原子平面配位的。As 2-二聚体（dAs-As = 250 μ m）存在于Pd 3As 8-层中。尽管每一层本身都有四重旋转对称性，但移位层堆叠导致了三斜空间群。La掺杂样品的电阻率测量表明，在17 K和零电阻率低于10 K的超导性的开始。在3.5 K时，磁屏蔽率约为20%. 57 Fe穆斯堡尔谱只有一条吸收线，没有显示出磁有序的迹象。电子结构与已知的铁砷化物非常相似，具有圆柱状费米表面和空穴和电子之间的部分嵌套。我们的研究结果表明，超导电性的钯-铁化合物是存在的，但复杂的太高的取代铁的钯在活性的FeAs层。由于电子的先决条件得到满足，我们预计较高的临界温度在Pd 1038-化合物与较低的或甚至没有Pd掺杂的FeAs层。
英文摘要：
The palladium-iron-arsenides Ca10(Fe1-xPdxAs)10(Pd3As8) were synthesized by solid state methods and characterized by X-ray powder and single crystal diffraction. The triclinic crystal structure (space group P-1) is isotypic to the homologue platinum 1038 type superconductors with alternating FeAs4/4- and Pd3As8-layers, each separated by layers of calcium atoms. Iron is tetrahedral and palladium is planar coordinated by four arsenic atoms. As2-dimers (dAs-As = 250 pm) are present in the Pd3As8-layer. Even though each layer itself has a fourfold rotational symmetry, the shifted layer stacking causes the triclinic space group. Resistivity measurements of La-doped samples show the onset of superconductivity at 17 K and zero resistivity below 10 K. The magnetic shielding fraction is about 20 % at 3.5 K. 57Fe-Mössbauer spectra exhibit one absorption line and show no hint to magnetic ordering. The electronic structure is very similar to the known iron-arsenides with cylinder-like Fermi surfaces and partial nesting between hole- and electron-like sheets. Our results show that superconductivity in the palladium-iron-compounds is present but complicated by too high substitution of iron by palladium in the active FeAs-layers. Since the electronic preconditions are satisfied, we expect higher critical temperatures in Pd1038-compounds with lower or even without Pd-doping in the FeAs-layer.
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