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Abstract: We present a first-principles study on a phase of BC7 with Amm2 space-group symmetry (we call o-BC7), which is selected from more than a dozen of candidates via energetic, mechanical and dynamical stabilities within a wide pressure scale from 0 to at least 100GPa. Our calculated results show that this structure is highly incompressible with large bulk and shear modulus of 388GPa and 430GPa, respectively, which is even higher than cubic BN. Further investigations revealed that the Vickers hardness (H v ≈49.5GPa) is higher than t-BC3 reported recently. And the superconducting critical temperature is calculated to be 38K, which is comparable to that of MgB2. [Copyright &y& Elsevier]

Abstract: C60 nanotubes have been synthesized by a solution–solution method. After degassing in a dynamic vacuum, the C60 nanotubes doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C60 nanotubes, forming A x C60 nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results. [Copyright &y& Elsevier]

Abstract: C60 microtubes were fabricated by a modified solution evaporation method, evaporating a solution of C60 in toluene in an atmosphere of m-xylene at room temperature. The C60 microtubes have outer diameters ranging from 2 to 8μm. IR spectra, TG analysis and X-ray diffraction showed a solvated structure for the as-grown C60 microtubes. Through a gentle heat-treatment in vacuum, pure C60 microtubes with single crystalline fcc structure were obtained after the elimination of solvents. It is suggested that the C60 microtubes form through self-assembly from several individual C60 nanorods. [Copyright &y& Elsevier]

Abstract: The effects of hydrostatic pressure on the formation enthalpy and electronic level positions of CN and CB in c-BN are investigated by means of ab initio plane-wave pseudopotential method using a supercell approach in the range of 0–60 GPa. The formation enthalpy decreases with pressure for CB, suggesting that CB becomes much more stable and has a larger concentration with pressure increase. In contrast to CB, the CN impurity exhibits positive dependence of the formation enthalpy on pressure, so the concentration of CN reduces with pressure. With pressure increase, the defect energy levels of CB +1 and CN –1 move into the conduction band and the valence band, respectively, while the defect energy levels of CB and CN in other charge states all move toward the center of band gap. These results suggest that pressure may make electron transfer between the impurity band and the conduction band or the valence band difficult and weaken its conductivity when a C atom substitutes at a B site or at a N site in c-BN. [Copyright &y& Elsevier]

Abstract: In this paper, C60 nanosheets with polymeric phases have been obtained under various high pressures and high temperatures, including orthorhombic and tetragonal polymeric phases. The structures have been identified and compared with those of nanorods by photoluminescence and Raman spectroscopies. The main fluorescence band shifted from 1.70 eV in the monomeric phase to near infrared in the polymeric phase when pressure and temperature were increased. The difference of photoluminescence and Raman spectra between nanosheets and nanorods samples treated under the same conditions is probably caused by different polymerization degree in these samples because of different shapes. [Copyright &y& Elsevier]