Superconductivity in graphite-potassium intercalation compound C8K

The critical temperature T_c, and the angular and temperature dependences of the upper critical field H_c2 in highly oriented pseudo-single crystals of C₈K have been studied by using a magnetic susceptibility measurement. The magnetic susceptibility abruptly changes around 139 mK at zero field. The angular dependence of H_c2 shows a very large anisotropy.     

Different electronic structures of C6Li and C8K graphite intercalation compounds studied by positron annihilation

The 2λ-angular correlation distributions of the stage 1 Graphite Intercalation Compounds C₆Li and C₈K are found to be very different. For C₈K, the distributions are dominated by a free electron contribution similar to those in pure alkali metals. In contrast, the distributions of C₆Li remain similar to those of graphite. The two materials are classified into s(+ π)-band metals (C₈K) and π-band metals (C₆Li).     

Magnetic properties of Europium-graphite intercalation compound C6Eu

An ordered state with a complex magnetic structure has been observed below 4CK. The magnetization for H ⊥ c (c; the c-axis) shows a field-induced phase transition from a small magnetic moment state ( ～ 0.6μ_B) at lower fields to a larger moment one ( 2.2 - 2.5μ_B) above 25kG. The transition field depends on temperature and is found to be 5 - 2kG. The magnetization for H//c has only a sublinear field dependence. Above 40K the magnetic susceptibility obeys the Curie-Weiss law with θ = +1.3K and the molar Curie constant C_m = 6.78, which suggests that Eu ion is divalent in C₆Eu.     

Superconductivity of the graphite intercalation compounds KHgC8 and RbHgC8

Superconductivity was observed in the graphite intercalation compounds, KHgC₈ and RbHgC₈, using an AC induction technique. The transition temperatures were 1.90K and 1.44K for KHgC₈ and RbHgC₈ respectively. A full Meissner effect was observed for KHgC₈ with a temperature dependant anisotropy in critical field with a value of 25 ± 5 at T_c.     

High field magnetization of europium-graphite intercalation compound C6Eu

The whole magnetization curve of the first stage compound C₆Eu has been measured by using pulsed fields up to 400 kG below 40 K. For H ⊥ c, c being the crystal c-axis, four regions are observed in the magnetization curve; I) the initial magnetization region with an apparent moment of ～ 0.6micro_B per Eu ion (H < 12 kG), II) the intermediate region with nearly constant moment of 2.2 – 2.7 micro_B, which corresponds to $\text{1}\text{3}$ the full moment of Eu²⁺ ion (22 < H < 82 kG), III) the region of a linear field dependence (82 < H < 205 kG), and IV) the saturation region above 205 kG, where the saturation moment is found as 6.2 micro_B. For H//c, the magnetization increases monotonically and approaches to a saturation value corresponding to 6 micro_B above 240 kG.     

Superconductivity in the Nb2SnC compound

Nb₂SnC is a member of the large family of lamellar materials that crystallize in the hexagonal structure with space group P6₃/mmc, which are isomorphs with Cr₂AlC, also named H-phase. In spite of the great number of compounds, which belong to this family, the superconductivity has been reported only for two cases: Mo₂GaC and Nb₂SC. In this work, we show that superconductivity can be observed in Nb₂SnC depending on the synthesis method used. The quality of the superconductor is strongly dependent of the synthesis method and the optimal results were reached for samples synthesized at 2.5 GPa and 523±50 °C. This sample showed a critical temperature close to 7.8 K, revealed from magnetization and transport measurement, the highest critical temperature reported up to now for an H-phase.     

A new mechanism of magnetic anisotropy due to π-f exchange in graphite intercalation compound C6Eu

The origin of XY magnetic anisotropy observed in antiferromagnet C₆Eu is studied theoretically. A new mechanism of magnetic anisotropy due to the combined action of the π-f exchange and the spin-orbit interaction is proposed. It is shown that this mechanism overcomes the ordinary mechanism due to the crystal field in the case of a Eu²⁺ ion.     

Thermal stability of cubane C8H8

The reasons for the anomalously high thermal stability of cubane C₈H₈ and the mechanisms of its decomposition are studied by numerically simulating the dynamics of this metastable cluster at T = 1050–2000 K using a tight-binding potential. The decomposition activation energy is found from the temperature dependence of the cubane lifetime obtained from the numerical experiment; this energy is fairly high, E _a = 1.9 ± 0.1 eV. The decomposition products are, as a rule, either C₆H₆ and C₂H₂ molecules or the isomer C₈H₈ with a lower energy. Original Russian Text ? M.M. Maslov, D.A. Lobanov, A.I. Podlivaev, L.A. Openov, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 609–612.     

Superconductivity in the RexMo6S8

The rare earth molybdenum sulfides RE_xMo₆S₈ (RE = rare earth) have been synthesized and are found to be superconducting with a few exceptions. This result, which is surprising in view of the high concentration of magnetic ions, is correlated with the particular structure of these compounds based on on units of Mo₆S₈.     

Variable charge transfer and band structure of graphite intercalation compounds: C8nAsF5

Using measurements of oscillatory magnetoresistance, the charge transfer in stage 2 AsF₅-graphite is found to vary over the range f ? 30–45%. By following the change of Fermi surface areas with f, a more precise determination of the band structure is possible. The band parameters are nearly identical to those of pristine graphite.     

On the formation and decomposition of C7H8

The kinetics of reactions on the C₇H₈ surface were studied with state-of-the-art ab initio transition state theory (TST) and master equation methodologies. A priori predictions of the capture rate for C₆H₅ + CH₃ and for C₇H₇ + H are obtained from direct variable reaction coordinate TST simulations. These simulations employ small basis set CASPT2 interaction energies coupled with one-dimensional reaction path corrections based on higher level simulations for related reactions. For the C₇H₇ + H reaction, predictions are obtained for both the total rate and for the branching between toluene, o-isotoluene and p-isotoluene. A mapping of the low energy pathways for isomerization from these three C₇H₈ isomers identifies a number of processes with barriers at or below the dissociation threshold. Nevertheless, at combustion temperatures the dissociation rates are predicted to exceed the isomerization rates, and it is reasonable to treat the kinetics of each isomer as a simple single well association/dissociation equilibrium. Master equation simulations yield predictions for the temperature and pressure dependence of each of the recombination and dissociation processes, as well as for the C₇H₇ + H → C₆H₅ + CH₃ bimolecular reaction. These simulations implement collisional energy transfer probabilities based on the work of Luther and co-workers. The theoretical predictions are found to be in satisfactory agreement with the available experimental data for the photodissociation of toluene, the temperature and pressure dependent dissociation of toluene, and the reaction of benzyl radical with H. For the C₆H₅ + CH₃ recombination, the theoretical predictions exceed the experimental measurements of Lin and coworkers by a factor of 2 or more for all temperatures.     

7Li and 133Cs NMR parameters in C6Li and C8Cs intercalated oriented graphites

The absolute values of the Knight shift in C₆Li and C₈Cs, prepared from highly oriented pyrolytic graphite, are found to be very different. Comparison to the corresponding values of Li and Cs metal, however, shows that the Knight shift reductions are similar. Nevertheless, the origins of these reductions are different in accordance with the different electronic structures of these compounds.     

Superconductivity of the potassium graphite intercalation compounds

The stratified compound C₄K has been found to pass to a superconducting state with the onset of transition at T_c = 1.3 K.     

插层化合物Ag1/4TiSe2电子结构的第一性原理研究

采用基于密度泛函理论的平面波赝势方法,选用局域密度近似对Ag_1/4TiSe₂及TiSe₂的几何结构进行了优化和总能量计算.计算得到的晶格常量与实验结果符合较好,负的形成能表明有序Ag_1/4TiSe₂系统的稳定性.布居数、键长、能带结构和态密度的计算结果显示：Ag以较强的离子性结合于Ag_1/4TiSe₂中.Ag的插入使得半金属性的TiSe_{2关键词： 1/4}TiSe₂')" href="#">Ag_1/4TiSe₂ 电子结构 插层化合物 第一性原理计算     

Laser-induced fluorescence spectrum of matrix-isolated C6H8+

A laser-induced fluorescence excitation and resolved emission spectrum of the radical cation of 1,3,5-hexatriene has been observed in a Ne matrix. Analysis of these spectra yield vibrational frequencies for both the ground $\text{X}\text{?}{}^2\text{A}{}_{\mathrm{u}}$ and excited $\text{A}\text{?}{}^2\text{B}{}_{\mathrm{g}}$ states of the ion. Observations are reported concerning the photoionization process, emission quantum yield, and ion fragmentation. Matrix site effects and production in the gas phase are also discussed.     

High-resolution infrared spectra of spiropentane, C5H8

Infrared spectra of spiropentane (C₅H₈) have been recorded at a resolution (0.002 cm⁻¹) sufficient to resolve for the first time individual rovibrational lines. This initial report presents the ground state rotational constants for this molecule determined from the detailed analysis of the ν₁₆ (b₂) parallel band at 993 cm⁻¹. In addition, the determination included more than 2000 ground state combination-differences deduced from partial analyses of four other infrared-allowed bands, the ν₂₄(e) perpendicular band at 780 cm⁻¹ and three (b₂) parallel bands at 1540 cm⁻¹ (ν₁₄), 1568 cm⁻¹ (ν₅ + ν₁₆), and 2098 cm⁻¹ (ν₅ + ν₁₄). In each of the latter four cases, the spectra show complications; in the case of ν₂₄, these complications are due to rotational l-type doublings, and in the case of the parallel bands, the spectral complexities are due to Fermi resonance and Coriolis interactions of the upper states with nearby levels. The unraveling of these is underway but the assignment of many of these transitions permit the confident use of the ground state differences in determining the following constants for the ground state (in units of cm⁻¹): B₀ = 0.1394741(1), D_J = 2.461(1) × 10⁻⁸, D_JK = 8.69(3) × 10⁻⁸. For the unperturbed ν₁₆ fundamental, more than 3000 transitions were fit and the band origin was found to be at 992.53793(3) cm⁻¹. The numbers in parentheses are the uncertainties (two standard deviations) in the value of the last digit of the constants. Surprisingly, the very accurate B₀ value measured here is lower than the value (0.1418 cm⁻¹) calculated from an electron diffraction structure, instead of being higher, as expected. Where possible, the rovibrational results are compared with those computed at the anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set. These too suggest that the electron diffraction results are in question.