On possible semiconducting and superconducting phases in hexaboride alloys

Based on the fact that hexaborides exist within a certain range of valence-electron concentration possible solid solutions are proposed that allow a wide variation of physical parameters. Phases of the type Ln_{$\text{2}\text{3}$}³⁺B₆ and Na_{$\text{1}\text{2}$}Ln_{$\text{1}\text{2}$}³⁺B₆ should be magnetic semiconductors.     

Metallic/semiconducting ratio of carbon nanotubes in a bundle prepared using CVD technique

We present an investigation of the nature of single-walled carbon nanotubes (SWCNTs) in a bundle by resonant Raman spectroscopy. The calculation has been done for the three peak positions in radial breathing mode (RBM) spectra obtained by using a laser excitation wavelength (γ) of 633 nm from He-Ne laser on SWNT bundle sample prepared by chemical vapor deposition (CVD) technique using iron catalyst at 800°C. The detailed analysis in the present study is focused on peak positions 162 cm⁻¹, 186 cm⁻¹, and 216 cm⁻¹. The firs step of the analysis is to construct a list of possible (n, m) pairs from the diameters calculated from the RBM peak positions. The parameters of SWNTs studied gives in-depth understanding of many symmetry, resonance and characteristic properties of SWNT bundles. Our results indicate that the contribution of metallic SWNTs in the bundle is small at RBM peak positions 162 cm⁻¹, 186 cm⁻¹ and in agreement with pervious results at peak position 216 cm⁻¹.     

Electron attenuation lengths in fullerene and fullerides

Using X-ray photoemission measurements, we have determined the attenuation length of C 1s photoelectrons in C₆₀ film to be 21.5 Å with the incident photon energy of Mg Kα radiation. The inelastic mean free path calculated with the TPP-2M algorithm coincides fairly well with the experimentally determined attenuation length, indicating the validity of the algorithm to fullerene and fullerides. The inelastic mean free paths for some fullerides, i.e. K₃C₆₀, K₆C₆₀, Ba₄C₆₀, Sm_2.75C₆₀ and Sm₆C₆₀ are calculated to help the quantitative analyses of the photoemission spectra for these compounds.     

Sm富勒烯的价带光电子能谱

用紫外光电子能谱和同步辐射光电子能谱研究了Sm掺杂C₆₀薄膜的价带电子结构.Sm的价电子大部分转移给C₆₀，化学键以离子性为主.对于任何化学配比都没有观察到费米边，所以Sm富勒烯超导相在室温下为半导体性质.获得了很接近单相Sm_2.75C₆₀的样品在费米能级附近的电子态密度分布.固溶相的光电子发射与Sm_2.75C₆₀有明显区别.Sm_xC_{60关键词： 60}的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 价带光电子能谱 电子结构     

Sm富勒烯的芯态光电子能谱

用X射线光电子能谱研究了Sm掺杂的固态C₆₀相衍变和芯电子态.在Sm_xC₆₀中Sm的含量x小于0.5时，样品是固溶相；在x=0.5和x=2.75之间的掺杂阶段，样品是这两个相的混合.在x=2.75和x=6之间的高掺杂阶段未观察到相分离的X射线光电子能谱证据.Sm 4f, 4d的实验数据表明Sm的价态是+2.二价Sm 3d_5/2芯态谱线存在两个子峰. 关键词： 60的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 相结构 电子态 X射线光电子能谱     

Electron spin-lattice relaxation in layered cuprates and fullerides

A new technique of measuring extremely short electron spin-lattice relaxation times T₁～10^?6–10^?10 sec is developed and applied to study some oxide high-T_c materials, related compounds and fullerides RbC₆₀.     

μSR studies of the metallic alkali fullerides

We report ZF μSR measurements in Cs₁C₆₀ at low temperature and LF μSR in the superconductor Rb₃C₆₀. In Cs₁C₆₀, the internal magnetic field distribution is broad and static, and the relaxation at 1.9 K resembles that of a spin density wave. In Rb₃C₆₀, we observe a strong field dependence to the coherence peak in the LF relaxation rate of endohedral muonium ( Mu@C₆₀) at anomalously low field and a residual low temperature relaxation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nonadiabatic channels in the superconducting pairing of fullerides

We show the intrinsic inconsistency of the conventional phonon mediated theory of superconductivity in relation to the observed properties of Rb3C60. The recent, highly accurate measurement of the carbon isotope coefficient alpha(C) = 0.21, together with the high value of T(c) (30 K) and the very small Fermi energy E(F) (0.25 eV), unavoidably implies the opening of nonadiabatic channels in the superconducting pairing. We estimate these effects and show that they are actually the key elements for the high value of T(c) in these materials compared to the very low values of graphite intercalation compounds.     

Preparation and characterization of metal-doped carbon aerogel for supercapacitor

Carbon aerogel was prepared by polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst with a resorcinol to catalyst ratio of 500. Co-doped carbon aerogels were then prepared by an impregnation method with a variation of cobalt content (1, 3, 5, 7, 10, and 15 wt.%), and their performance for supercapacitor electrode was investigated by measurement of specific capacitance in 1 M H₂SO₄ electrolyte at a scan rate of 10 mV/s. Among the samples prepared, 7 wt.% Co-doped carbon aerogel showed the highest capacitance (100 F/g) and stable cyclability. The enhanced capacitance of Co-doped carbon aerogel was attributed to the faradaic redox reactions of cobalt oxide. On the basis of this result, 7 wt.% Cu-, Fe-, Mn-, and Zn-doped carbon aerogels were also prepared by an impregnation method for use as a supercapacitor electrode. Among the metal-doped carbon aerogels, Mn-doped carbon aerogel showed the highest capacitance (107 F/g) while Cu- and Fe-doped carbon aerogels exhibited the most stable cyclability.     

Structural features of the polymer-like phase of AC60 fullerides

A new approach is proposed for describing the deformation of the C₆₀ molecule in the polymer-like phase of the fullerides AC₆₀ (A=K, Rb). A discrete basis of orientational states of the molecule is introduced, and orientational ordering is described on the basis of a phenomenological theory. A symmetry analysis of the molecular vibrations in the Fm3m phase is performed. It is shown that small rotations of the C₆₀ can occur at a phase transition. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 110–115 (25 July 1996)     

Characteristics and heterostructure of metal-doped TiO2/ZnO nanocatalysts

In this study, Ag or Al-doped TiO₂/ZnO heterostructure nanocatalysts were prepared using a sol-gel method for photocatalysis to evaluate the degradability. The photocatalytic behavior was evaluated by the degradation of methylene blue (MB) under ultraviolet (UV) light irradiation. Photocatalytic studies suggested that 1 mol% Ag-doped TiO₂/ZnO (TiO₂/ZnO = 0.75/0.25) heterostructure nanocatalysts showed higher photocatalytic activity, and that the degradation efficiency can reach 83% in 4 h, 14% higher than that for pure TiO₂. Finally, the photocatalysis mechanism for the Ag-doped TiO₂/ZnO heterostructure nanocatalysts is discussed.     

3d过渡金属掺杂锐钛矿相TiO2的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法研究了纯锐钛矿相TiO₂及掺杂3d过渡金属TiO₂的几何、电子结构及光学性质. 计算结果表明掺杂能级的形成主要是掺杂过渡金属3d轨道的贡献，掺杂能级在禁带中的位置是决定TiO₂吸收带边能否出现红移的重要因素. Cr，Mn，Fe，Ni，Co，Cu掺杂使TiO₂的吸收带边产生红移，并在可见光区有一定的吸收系数； Sc，Zn掺杂使TiO₂的吸收带边产生蓝移，但在可见光区有较大的吸收系数；掺V不但使TiO₂的吸收带边产生红移，增强了在紫外光区的光吸收，而且在可见光区有非常大的吸收系数.