Xuanjia Zhang

New method of carbon onion growth by radio-frequency plasma-enhanced chemical vapor deposition

Large quantities of carbon onions with high purity were synthesized by radio-frequency plasma-enhanced chemical vapor deposition. The produced carbon onions are solid, clean and can be separated easily from the catalytic particles. The formation of onions is based on the formation of many cages in successive stages from the core to the surface. Around the edge of a carbon onion, discontinuous curved lines are shown in the high-resolution TEM image, reflecting the wavy behavior of carbon onions.

Generation of curved or closed-shell carbon nanostructures by ball-milling of graphite

Abstract Curved or closed-shell carbon nanostructures were produced by ball-milling of graphite. A high resolution indicates that the ball-milling not only produces bend of graphite sheets, forming carbon nanoarches, but also produces closed-shell carbon nanostructures, nearly carbon ‘onions’. The possible formation mechanism is proposed.

Preparation, morphology and microstructure of segmented graphite nanofibers

Abstract Vapor-grown of segmented graphite nanofibers were prepared by pyrolysis of acetylene at 600–800°C using a foam Ni catalyst. Through transmission electron microscopy observation, it was found that this kind of nanofiber looks like a line of lens-like segments with nearly equal separation, which consist of well-ordered graphite platelets intermittently stacked perpendicularly to the filament axis. It was suggested that the catalyst particles adopting a thin slice shape and the flow rate of acetylene are critical for forming segmented graphite nanofibers. The formation mechanism of segmented graphite nanofibers has also been discussed.

Growth of well-crystallized segmented graphite nanofibers by catalytic chemical vapor deposition

Abstract Well-crystallized segmented graphite nanofibers were prepared by pyrolysis of acetylene at 600–800°C using foam Ni catalyst. Transmission electron microscopy indicates that this kind of nanofiber looks like a linear array of lens-like segments with nearly equal separation, which consist of well-ordered graphite platelets intermittently stacked perpendicularly to the filament axis. It was found that the catalyst particles adopting thin slice shape and the flow rate of acetylene are critical for forming segmented graphite nanofiber. The formation mechanism of segmented graphite nanofiber is also discussed.

Growth and characterization of Sr-rich Pr(Sr, Ba)2Cu3Oy single crystals

Abstract We have grown large Sr-rich Pr(Sr,Ba) 2 Cu 3 O y single crystals using SrO-BaO-CuO mixture as the self-flux. The crystals were characterized by energy dispersive X-ray spectrometry, X-ray diffraction, temperature dependence of resistivity and susceptiblity, and thermal analysis. This high Sr content is probably due to Al incorporation from the Al 2 O 3 crucible. Our growth approach may provide an alternative to the preparation of twin-free 123 crystals.

The Ba-site Pr substitution effects in YBa2−xPrxCu3O7−δ system

Abstract The measurements of X-ray diffraction, electrical resistivity, Hall effect and thermopower were performed in single-phase YBa 2−x Pr x Cu 3 O 7−δ cuprates. It was found that the suppression of T c is mainly caused by the decrease of p H , and there are no strong evidence for pair-breaking effects of Ba-site Pr ions.

Observation of anisotropy of in-plane resistivities in PrBa2Cu3O7 single crystals

Abstract We report the anisotropic resistivities of PrBa 2 Cu 3 O 7 single crystals. It was observed that both ϱ a and ϱ b exhibit semiconducting behavior, but ϱ a is 10 times higher than ϱ b at room temperature. The anisotropic behavior of the in-plane resistivity suggests the conductivity contribution from the CuO chains in PrBa 2 Cu 3 O 7 . We also analyze the results in terms of the variable-range-hopping model.

The photoemission study of intermetallic compound superconductor YNi2B2C

Abstract The photoemission spectrum was measured on YNi 2 B 2 C and was found to be well coincident with calculation except in the vacinity of E F . The DOS peak at E F predicted by band theory has not been detected. The author suggests that the low energy excitation which is responsible for the suppression of DOS at E F , is responsible for the pairing of superconductivity as well.

Synthesis and superconductivity of a new type of 1212 phase cuprate (B,Cd)(Sr,Ba)2YCu2Oy

Abstract A new type of 1212 phase cuprates (B,Cd)Sr 2 YCu 2 O y has been synthesized by solid state reaction. In the (B 0.5 Cd 0.5 )Sr 2−x Ba x YCu 2 O y system, Ba substitution induces superconductivity, with the optimum T c of 60K for x=0.6. The nonmonotonic variation of T c with Ba content is discussed.

Transport and Electronic Properties of Y0.4Pr0.6Ba2-ySryCu3O7-δ (y=0,1.0)

We report measurements of the resistivity, thermoelectric power and Hall carrier number on Y0.4Pr0.6Ba2-ySryCu3O7-δ (y=0, 1.0) polycrystalline samples. The Sr-free compound exhibits semiconducting behavior, while the Sr-doped sample is superconducting at 18 K with a possible pseudo-gap structure at 255 K. Results of the thermoelectric power and Hall measurements revealed that the revival of superconductivity by the Sr substitution is due to the increase of mobile hole-concentration. We present a band picture of Pr4f–O2p hybridization to elucidate the variation of the transport properties.