Investigation on the silicon network solids and related materials

我们研究了硅网络固体和相关材料，并获得了以下结果。(1)发现硅笼形超导体Ba_8Si_3<46>在超导态下具有自旋-自旋弛豫速率1/T_2和奈特位移的反常行为。(2)证实了Si_2超导体中费米能级上电子态密度的尖峰是导致超导现象发生的原因<46>。该峰是由于Si和Ba轨道之间的杂化。(3)本文<60>用核磁共振方法系统地研究了具有大、小晶格常数的A_3C_2化合物，如（NH_3）<60>A_3C_2、Na_2AC_3<60>和Li_xAC_3<60>（A为碱金属）。t轨道<1u>简并度对金属态的稳定性有重要影响，它的分裂和轨道有序化导致反铁磁基态的形成。(4)用核磁共振和磁化率研究了一种新的层状超导体HfNCl。结果表明，HfNCl是一种二维超导体，在费米能级上具有非常小的态密度。这表明，超导电性不能用传统的机制来解释。(5)通过X射线衍射测定了MWNT和SWNT的热膨胀。首次发现氢气氛下生长的多壁碳纳米管样品中含有大量封闭的俄罗斯娃娃管。(6)用<60>NMR研究了含Li和Na的C_聚合物。结果表明，晶体中存在与所提出的结构一致的sp^3碳原子，并且碱金属离子在晶体中移动。(7)用核磁共振研究了骨架结构与Si_（46）笼形物相似的碱负载沸石LTA的低温铁磁性。1H <29>Si NMR为我们提供了有关磁矩分布的信息。

We investigated silicon network solids and related materials, and obtained the following results.(1) Silicon clathrate superconductor, Ba_8Si_<46> was found to show anomalous behaviors of spin-spin relaxation rate 1/T_2 and Knight shift in the superconducting state.(2) It was confirmed that the sharp large peak of the electronic density of states at the Fermi level is responsible for the occurrence of superconductivity in Si_<46> superconductors. The peak is due to a hybridization between Si and Ba orbitals.(3) A_3C_<60> compounds with large and small lattice constants, such as (NH_3)A_3C_<60>, Na_2AC_<60> and Li_xAC_<60> where A is alkali metals, were systematically investigated by NMR. The t_<1u> orbital degeneracy is important for the stability of the metallic states, and that its splitting and orbital ordering lead to antiferromagnetic ground states.(4) A new layered superconductor, HfNCl, was investigated by NMR and magnetic susceptibility. It was found that HfNCl is a two-dimensional superconductor with a very small density of states at the Fermi level. It was suggested that the superconductivity cannot be explained by the conventional mechanisms.(5) Thermal expansion of MWNT and SWNT was determined by means of x-ray diffraction. MWNT sample grown in hydrogen atmosphere was found to contain a lot of closed Russian doll type tubes for the first time.(6) C_<60> Polymers including Li and Na were investigated by NMR. It was shown that there are sp^3 carbon atoms consistent with proposed structures, and that the alkali ions are moving in the crystals.(7) Alkali-loaded zeolite LTA, whose framework structure is similar to that of the Si46 clathrates, was studied by NMR to clarify the origin of the ferromagnetism at low temperature in this system. The ^<29>Si NMR gave us information on the distribution of the magnetic moments.