Preparation and Properties of Layer Structured High-Tc Superconductors

1. 层状结构的氮化物β-MNCl（M = Zr，Hf）可以通过嵌入锂进行电子掺杂，并转变为超导体，当M = Zr和Hf时，超导转变温度（Tc）分别为14和25.5 K。通过极性溶剂分子与锂离子的共嵌入可以控制层间距，超导的各向异性大大增强。核磁共振和μ子自旋关系测量表明，电子掺杂层结构氮化物超导体具有以下特性： (i) 高度各向异性的奇异超导体，(ii) 费米能级附近的低载流子密度，〜10^<21>/cm^3，(iii) 对 ^<15>N 替代的同位素效应非常小，以及 (iv) 低声子激发。超导性是非常规的。2．层状结构的氮化物氯化物 β-MNCl (M = Zr, Hf) 晶体非常薄且柔软，很难用于 X 射线结构分析和物理性质测量。我们成功开发了一种新的高压合成方法，以氯化铵为熔剂获得厚单晶。还获得了各种β-MNX（M = Zr，Hf；X = Cl，Br，I）的单晶，并通过X射线单晶分析确定了晶体结构。结果发现化合物结晶为两种不同的多型体：SmSI和YOF结构。 3．为了尝试定制新型层状结构氮化物化合物，在超高真空条件下使用电子束蒸发和激光烧蚀方法以及氮自由基源制备了人造氮化物薄膜。在 MgO (100) 衬底上外延生长氮化钛 (TiN) 薄膜，并通过 RHEED 成功监测逐层生长。 CrN可以外延沉积在Si(100)上，随后在CrN薄膜上外延生长NbN薄膜。这一发现表明合成具有超结构的人造 CrN-NbN 薄膜的可能性。较少的

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