Xianhui Chen

A simple direct preparation of nanocrystalline γ-Mn2O3 at ambient temperature

Abstract Nanocrystalline γ-Mn2O3 has been prepared directly by the reduction of aqueous KMnO4 with hydrazine solution at ambient temperature, without post-treatment of heating. X-ray powder diffraction (XRD) pattern demonstrates its good phase purity. Transmission electron microscopy (TEM) images show homogeneous nanoparticles with a narrow size distribution. The average grain size is about 9 nm. The evolution of crystallite size upon the annealing temperature was investigated. The effect of various reaction factors, e.g., pH, concentration of N2H4 and additants, on the nature of products was also investigated.

Synthesis and characterization of reduced transition metal oxides and nanophase metals with hydrazine in aqueous solution

Reduction of the first row (3d) transition metal complexes in aqueous solution using hydrazine as the reducing agent has been investigated systematically. Nanoscale reduced metal oxides such as VO2(B), Cr2O3 were obtained through hydrazine reduction followed by proper thermal treatments. Nanocrystalline γ-Mn2O3 was synthesized directly through aqueous phase reduction at room temperature. Nanoclusters of cobalt, copper and the one-dimensional single crystal nickel nanowhiskers were synthesized by direct reduction without post-annealing process. All the products were characterized on their structure and micro-morphology. The reaction details and features were described and discussed.

Same superconducting criticality for underdoped and overdoped La2-xSrxCuO4 single crystals

By measuring the superconducting diamagnetic moments for an underdoped and an overdoped La2-xSrxCuO4 single crystal with equal quality and roughly equal transition temperatures, it is found that the underdoped sample has only one transition which corresponds to H(c2), but the overdoped sample has two transitions with the higher one at H(c2). Further investigation reveals the same upper-critical field H(c2) for both samples although the overall charge densities are very different, indicating the possibility of a very direct and detailed equivalence of the superconducting condensation process in the two doping limits. The second transition for the overdoped sample can be understood as the bulk coupling between the superconducting clusters produced by macroscopic phase separation.

Two-bandgap magneto-thermal conductivity of polycrystalline MgB2

The thermal conductivity κ(B,T) of polycrystalline superconducting MgB2 has been studied as a function of temperature (from 4 up to 50 K) and (up to a rather large 14 T) applied magnetic field. No anomaly in the thermal conductivity κ(B,T) is observed around the superconducting transition in the absence or presence of magnetic fields up to 14 T; at that field value the superconductivity of MgB2 persisted. The thermal conductivity in zero field shows a T-linear increase up to 50 K. The thermal conductivity is found to increase with increasing field at high fields. We interpret the findings as if there are two subsystems of quasiparticles with different field-dependent characters in a two- (L- and S-) band superconductor reacting differently with the vortex structure. The unusual enhancement of κ(B,T) at low temperature but higher than a ( T) critical field is interpreted as a result of the overlap of the low energy states outside the vortex cores in the S band. An order of magnitude of the Bc2S temperature dependence is given, in agreement with recent results by other authors under different experimental conditions.The thermal conductivity

Synthesis and structure of BaxC70

\kappa (H,T)

Superconductivity and specific heat of Ru1-xTaxSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2Oy

of the new superconductor

Hydrothermal synthesis and characterization of nanorods “LixV2−δO4−δ·H2O”

MgB_2

Large distinctions between underdoped and overdoped La2−xSrxCuO4 single crystals as observed from magnetic and transport measurement: A possible evidence for macroscopic phase separation in overdoped high temperature superconductors

was studied as a function of the temperature and a magnetic field. No anomaly in the thermal conductivity

Electronic Properties of Ba-Intercalated Fullerides

\kappa (H,T)

The carrier characteristics of single phase superconducting oxides (Bi, Pb)2Sr2Ca2Cu3Oy under different heat treatments

is observed around the superconducting transition in absence or presence of magnetic fields up to 14 Tesla; upon that field the superconductivity of