Yuanbin Qin

Synthesis of β-SiC nanowires with SiO2 wrappers

β-SiC nanowires with uniform amorphous SiO2 wrappers have been synthesized by carbothermal reduction of the sol-gel derived silica containing carbon nanoparticles. The product was characterized by IR, TEM, HREM, and EDX. The nanostructures are more than 20 μm in length. The diameters of β-SiC nanowires are in the range 10–25 nm, while the outer diameters of the SiO2 wrappers are between 20 and 70 nm. The formation of β-SiC nanowires is ascribed to the large quantities of SiC nuclei and the nanometer-sized SiC nucleus sites on carbon nanoparticles. The SiO2 wrappers come from the combination reaction of the SiO vapor and O2 decomposed from the unreacted SiO2.

Nonlinear current-voltage behavior and electrically driven phase transition in charge-frustrated LuFe2O4

Electric transport measurements of the charge-frustrated LuFe2O4, in which charge ordering (CO) and electronic ferroelectricity are found, reveal a strong nonlinear electric conduction upon application of electric fields in both single-crystalline and polycrystalline samples. The threshold electric fields (Et) in LuFe2O4 are estimated to be about 60u2009V/cm and 10u2009V/cm with E parallel and perpendicular to the c-axis direction, respectively. Experimental measurements also demonstrate that the I-V nonlinearity increases quickly with decreasing temperature. Furthermore, our in situ TEM investigations clearly reveal that the nonlinear I-V behavior is intrinsically in correlation with a current-driven charge ordering insulator-metal transition, and the applied electrical field triggers a visible CO collapse recognizable as the fading of the satellite spots of the CO modulations.

Synthesis of “A β-SiC nanorod within a SiO2 nanorod” one dimensional composite nanostructures

Abstract “A β-SiC nanorod within a SiO 2 nanorod” one dimensional composite nanostructures were synthesized by the combination of a low temperature (1650°C) carbothermal reduction and a high temperature (1800°C) heating of sol-gel derived silica xerogels containing carbon nanoparticles. The composite nanostructures are more than 20 μm in length. The diameters of the center thinner β-SiC nanorods are typically in the range 10–30 nm, while the outside diameters of the corresponding thicker amorphous SiO 2 nanorods are between 20 and 70 nm. Large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are both favor-able to the formation of much thinner β-SiC nanorods. The formation of the outer coaxial thicker amorphous SiO 2 nanorods is from the combination reaction of decomposed SiO vapor and O 2 during cooling.

Structural properties and superconductivity of SrFe2As2 − xPx (0.0 ≤ x ≤ 1.0) and CaFe2As2 − yPy (0.0 ≤ y ≤ 0.3)

The SrFe(2)As(2 - x)P(x) (0.0 ≤ x ≤ 1.0) and CaFe(2)As(2 - y)P(y) (0.0 ≤ y ≤ 0.3) materials were prepared by a solid-state reaction method. X-ray diffraction measurements indicate that the single-phase samples can be successfully obtained for SrFe(2)As(2 - x)P(x) (0.0 ≤ x ≤ 0.8) and CaFe(2)As(2 - y)P(y) (0.0 ≤ y ≤ 0.3). Visible contraction of the lattice parameters is determined due to the relatively smaller radius of P ions in comparison with that of As. The spin-density-wave (SDW) instability associated with the tetragonal to orthorhombic phase transition is suppressed noticeably in both systems following the increase in P content. The highest superconducting transitions are observed at about 27xa0K in SrFe(2)As(1.3)P(0.7) and at about 13xa0K in CaFe(2)As(1.925)P(0.075), respectively. Structural analysis suggests that lattice contraction could notably affect the superconductivity in these materials.

Quaternary pyrite-structured nickel/cobalt phosphosulfide nanowires on carbon cloth as efficient and robust electrodes for water electrolysis

The strategy of element substitution is an effective way to tune the electronic structures of the active sites in catalysts, thereby leading to improvements in both the catalytic activity and stability. Herein, we design and synthesize pyrite-type nickel/phosphorus co-doped CoS2 nanowires on carbon cloth (NiCoPS/CC) as efficient and durable electrodes for water electrolysis. Introduction of nickel and phosphorus produced stepwise and superb enhancement of the performance of the electrodes in the hydrogen evolution reaction due to regulation of the electronic structures of the active sites of the catalyst and accelerated charge transfer over a wide pH range (0−14). The NiCoPS/CC electrodes also delivered a nearly undecayed catalytic current density of 10 mA·cm−2 at a low overpotential of 230 mV for oxygen evolution due to in situ formation of surficial Ni–Co oxo/hydroxide in 1.0 M KOH. Thus, the NiCoPS/CC electrodes gave rise to a catalytic current density of 10 mA·cm−2 for overall water splitting at potentials as low as 1.54 V during operation over 100 h in 1.0 M KOH with a Faradic efficiency of ~100%.

Nonlinear transport properties and Joule heating effect in charge ordered LuFe2O4

The nonlinear current-voltage (I-V) relation of charge ordered (CO) LuFe2O4 has been studied in the temperature range from 220 to 520 K. Strong nonlinear effects are identified in the CO state and disappear in high-temperature charge disordered state. Alternation of the CO state under applied electric field is directly revealed by in situ transmission electron microscopy observations. Careful investigations of time-dependent resistance under the applied electric field near the threshold value (Eth) often show three distinct steps for the nonlinear transitions. The CO collapse likely at a critical conductivity yields a sharp drop in resistance.

Suppression of the current leakage in charge ordered Lu2Fe2Fe1−xMnxO7 (0<x≤0.86)

The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1−xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization–electric field switching curves. The charge ordering states in Lu2Fe2Fe1−xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.

The effect of Mg doping on the structural and physical properties of LuFe2O4 and Lu2Fe3O7

The structural and physical properties of the recently discovered electronic ferroelectric materials LuFe(2)O(4) and Lu(2)Fe(3)O(7) have been investigated for Mg substitution of Fe. X-ray diffraction data demonstrate that the lattice parameters in both systems change progressively with increasing Mg content, with a smaller unit cell volume on replacing Fe(2+) by Mg(2+). X-ray absorption near-edge spectroscopy experiments at the Fe K-edge show that the average Fe oxidation state is slightly increased along with Mg doping in Lu(2)Fe(3)O(7) materials, consistent with isomorphous replacement of Fe(2+) by Mg(2+). Measurements of dielectric properties demonstrate that Mg doping could have an effect on the electron hopping energy between Fe(2+) and Fe(3+) ions. Transmission electron microscopy and magnetization analysis reveal that Mg doping in LuFe(2)O(4) has a much greater influence than in Lu(2)Fe(3)O(7) on both the charge ordering and the low-temperature magnetic properties.

β-SiC nanorods with uniform amorphous SiO2 wrappers on the outside surface

Abstract Large quantities of β-SiC nanorods with uniform amorphous SiO2 wrappers were synthesized by carbothermal reduction of silica xerogel pieces with carbon nanoparticles embedded in the network. Powder X-ray diffraction (XRD) and infrared (IR) results confirmed the formation of β-SiC and SiO2. Low-magnification transmission electron microscopy (TEM) results showed that the nanorods were typically more than 20 μm in length. High-magnification TEM and high-resolution electron microscopy (HREM) indicated that the β-SiC nanorods (with typical diameters of 14 ± 6 nm) were wrapped in amorphous SiO2 layers (with typical outside diameters of 45 ± 25 nm).

Spontaneous formation of circular and vortex ferroelectric domain structure in hexagonal YMnO3 and YMn0.9Fe0.1O3 prepared by low temperature solution synthesis

We report an experimental study of the domain structure of ferroelectric YMnO3 and YMn0.9Fe0.1O3 using polycrystalline samples prepared by direct hydrothermal crystallisation at 240u2009°C, well below their structural phase transition temperatures. Powder X-ray diffraction shows the expected P63cm space group for both samples with an increase in a and a small decrease in c with Fe incorporation, consistent with an adjustment of MnO5 tilting, while XANES spectra at the Mn and Fe K edges show the oxidation state of both metals are maintained at +3 in the doped sample. High resolution TEM shows that curved stripe, annular and vortex domains can all be observed in the YMnO3 crystals, proving that the structural phase transition is not the only driving force for the occurrence of the annular and vortex domains. Furthermore, the absence of the annular and vortex domains in YMn0.9Fe0.1O3 indicates that the tilting state of MnO5 bipyramids plays an important role in the domain formation. Atomic resolution STEM images...