Preparation and Properties of Layer Structured High-Tc Superconductors

1. 层状结构氮化物β-MNCl （M = Zr, Hf）可以通过锂的插入进行电子掺杂，并转变为超导体，M = Zr和Hf的超导转变温度分别为14和25.5 K。极性溶剂分子与锂离子共插层可以控制层间间距，大大增强了超导的各向异性。核磁共振和介子自旋关系测量表明，电子掺杂层状结构氮化物超导体具有以下特征；(i)高度各向异性的外来超导体，（ii）费米能级附近载流子密度低，~ 10^<21>/cm^3, （iii）同位素对^<15>N替代的影响很小，以及（iv）低声子激发。超导性是很不寻常的。层状结构的氮化物氯化物，β-MNCl （M = Zr, Hf）是非常薄和柔软的晶体，很难用于x射线结构分析和物理性质测量。我们成功地开发了一种以氯化铵为助熔剂制备厚单晶的高压合成新方法。以单晶形式得到了各种β-MNX (M = Zr, Hf; X = Cl, Br， I)，并通过X射线单晶分析确定了晶体结构。发现化合物结晶成两种不同的多型结构：SmSI结构和YOF结构。在超高真空条件下，利用氮自由基源，采用电子束蒸发和激光烧蚀的方法制备了新型层状结构氮化物薄膜。在MgO（100）衬底上外延生长了氮化钛（TiN）薄膜，并通过RHEED成功地监测了其逐层生长。CrN可以外延沉积在Si（100）上，随后在CrN薄膜上生长出外延的NbN薄膜。这一发现提示了合成具有超结构的人造CrN-NbN薄膜的可能性。少

1. The layer structured nitride chlorides, β-MNCl (M = Zr, Hf) can be electron-doped by the intercalation of lithium, and are changed into superconductors with the superconducting transition temperatures (Tc's) of 14 and 25.5 K for M = Zr and Hf, respectively. The interlayer spacing can be controlled by the co-intercalation of polar solvent molecules with lithium ions, and the anisotropy of the superconductivity is greatly enhanced. The NMR and muon spin relation measurements revealed that the electron-doped layer structured nitride superconductors have the following characteristics ; (i) highly anisotropic exotic superconductors, (ii) low carrier density near Fermi level, 〜10^<21>/cm^3, (iii) very small isotope effect on the replacement with ^<15>N, and (iv) low phonon excitation. The superconductivity is very unconventional.2. The layer structured nitride chlorides, β-MNCl (M = Zr, Hf) were so thin and so soft crystals that it was very difficult to use for X-ray structural analysis a … More nd physical property measurements. We have succeeded to develop a new high pressure synthesis method to obtain thick single crystals using ammonium chloride as flux. All kinds of β-MNX (M = Zr, Hf ; X = Cl, Br, I) were also obtained as single crystals, and the crystal structures were determined by X-ray single crystal analyses. It was found that the compounds were crystallized into the two different polytypes, the SmSI and the YOF structures.3. In an attempt to tailor new layer structured nitride compounds, thin artificial nitride films were prepared using electron-beam evaporation and lazer ablation methods with a nitrogen radical source under ultrahigh vacuum conditions. Titanium nitride, TiN, films were epitaxially grown on MgO (100) substrates, and the layer-by-layer growth was successfully monitored by RHEED. CrN could be epitaxially deposited on Si(100), and an expitaxial NbN film was subsequently grown on the CrN film. This finding suggests the possibility of the synthesis of artificial CrN-NbN films with superstructures. Less