Jiaju Du

Crystalline gallium oxide nanowires: intensive blue light emitters

Abstract Gallium oxide nanowires (GaONWs; diameter, ca. 60 nm; length, hundreds of micrometers) have been synthesized by a carbothermal reduction reaction. The nanowires have been confirmed as crystalline β -Ga 2 O 3 by powder X-ray diffraction and selected area electronic diffraction. The GaONWs can emit stable and high brightness blue light at 446 nm (2.78 eV) under excitation at 378 nm (3.28 eV), which may have potential applications in one-dimensional optoelectronic nanodevices.

Preparation and photoluminescence properties of amorphous silica nanowires

Abstract Bulk-quantity amorphous silica nanowires (SiONWs) have been synthesized by carbothermal reduction reaction between silicon dioxide and active carbons. Transmission electron microscopy (TEM) image shows the formation of the nanowires at a diameter of 60–110 nm and a length up to hundreds micrometers. Besides most smooth-surface polyp-shaped nanowires, two other forms of nanowires, named amoeba-shaped and frog-egg-shaped nanowires, have also been observed. The nanowires can emit stable and high brightness blue light at 435 nm (2.85 eV) under excitation at 260 nm (4.77 eV). The formation of the nanowires into different shapes may be explained by the vapor–liquid–solid (VLS) mechanism.

Preparation and photoluminescence properties of crystalline GeO2 nanowires

Abstract Bulk-quantity GeO 2 nanowires (GeONWs) have been synthesized by carbothermal reduction reaction between germanium dioxide and active carbons. Transmission electron microscopy (TEM) image shows the formation of the nanowires at a diameter about 50–120 nm and a length up to hundreds of micrometers. The nanowires can emit stable and high brightness blue light at 485 nm (2.56 eV) under excitation at 221 nm (5.61 eV). The intensity of the emission is one order of magnitude higher than that of GeO 2 powders. The photoluminescence (PL) may originate from radiative recombination between an electron on V O × and a hole on ( V Ge , V O ) × in the GeONWs. The nanowires may have potential applications in one-dimensional optoelectronic nanodevices.

Large room-temperature magnetoresistance and phase separation in La1−xNaxMnO3 with 0.1⩽x⩽0.3

The structural, magnetic, and electronic properties of the polycrystalline La1−xNaxMnO3 (x=0.10, 0.15, 0.20, and 0.30) are investigated. The result of the Rietveld refinement of x-ray powder diffraction shows that these compounds crystallize in a rhombohedrally distorted structure with space group R3C. The magnetic measurement shows that Curie temperature TC of the studied samples is near or above room temperature. The temperature dependence of resistivity shows that all samples undergo a sharp transition accompanying a paramagnetic to ferromagnetic with the decrease of temperature, however, for x⩾0.15 samples, double transition peaks with a single ferromagnetic transition is observed. In the meanwhile, a large room-temperature magnetoresistance with low applied magnetic field is observed. The co-existing ferromagnetic metallic phases and ferromagnetic insulating (FMI) phases induced by the electronic inhomogeneity as well as the additional FMI phases caused by the presence of vacancies at the A sites, a...

Simultaneous growth of α-Si3N4 and β-SiC nanorods

Abstract Well-separated α-Si 3 N 4 and β-SiC nanorods have simultaneously been synthesized by the reaction of SiO 2 nanoparticles and active carbon at 1450°C in nitrogen atmosphere. TEM (transmission electron microscopy) photographs confirm α-Si 3 N 4 nanorods with the diameter of 10–100 nm and length up to 15μm, and β-SiC nanorods with the diameter around 40 nm and length up to about 1 μm. The chemical reaction conditions and mechanisms have been discussed.

Structural, magnetic, and transport properties in a Cu-doped La0.7Ca0.3MnO3 system

The structural, magnetic, and transport properties of La0.7Ca0.3Mn1−xCuxO3 (0⩽x⩽0.2) have been investigated. The maximum magnetoresistance (MR) is about 4×106% for the sample with x=0.15, which is about ∼104 times the maximum MR for samples with x⩽0.1. A change in the structural parameters and magnetic and resistivity properties of the samples shows that Cu exists in Cu3+ ionic form in the sample with x⩽0.05. However, Cu2+ ions begin to appear and then they increase with further Cu doping.

Enhanced flux pinning in (Bi, Pb)-2223/Ag tapes by slight Pr substitution

Bi1.8Pb0.4Sr2Ca2.2-xPrxCu3Oy silver sheathed ((Bi, Pb)-2223/Ag) tapes with x = 0.0 (un-doped), 0.001 and 0.002 (Pr doped) have been investigated. X-ray diffraction analyses and transmission electron microscopy observation show that in the Pr-doped tapes there are many defective regions induced by the partial Pr substitution for Ca with a size of about 10 nm. As compared with the un-doped tape, the magnetic field dependence of critical current densities of the Pr-doped tapes are noticeably improved at 77 K. Their irreversibility lines are also shifted to higher temperatures and magnetic fields, and their activation energies of flux motion are increased drastically. The pinning force densities of the tapes are fitted with a improved law from the Dew-Hughes model; the results of this fitting show that the flux pinning enhanced in Pr-doped tapes mainly originates from the fine normal-like defects.

Nano-MgO particle addition in silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes

Abstract Nano-MgO particles have been introduced into Bi-2223/Ag tapes fabricated by the rod-in-tube process. The effect of MgO on the high- T c (Bi-2223) phase formation, microstructure and transport property of the tapes was studied. The DTA measurements showed that the nanometer MgO particles decreased the optimum sintering temperature of the tapes. XRD and SEM analysis indicated that nano-MgO particle increased the low- T c (Bi-2212) phase fraction in the tapes and degraded the grain alignment. The electrical and magnetic measurements showed that nano-MgO had little effect on the critical temperature ( T c ) of the tapes. The critical current density ( J c ) of the tapes with moderate MgO doping (∼2.5×10 4 A/cm -2 ) was higher than that of undoped tapes (∼2×10 4 A/cm -2 ). The J c behavior of doped samples in magnetic field was significantly improved.

Enhanced flux pinning of Bi-2223/Ag tapes with nano-MgO particles addition

For the purpose of producing flux pinning centers, nano-MgO particles have been introduced into (Bi,Pb)2)Sr2Ca2Cu3Ox silver-sheathed (hereafter: Bi-2223/Ag) tapes fabricated by the Rod-In-Tube (RIT) process. It is found that transport critical current density (Jc) of samples doped with nano-MgO particles is higher than that of undoped samples by a factor of 1.2 in zero applied field and about 1.4 in a magnetic field range from 0.1 to 1 T at 77 K. Well-dispersed MgO particles can be observed by SEM. These results indicate that the introduction of nano-MgO particles can effectively improve the flux pinning ability and has a little detrimental effect on the Bi-2223 superconducting matrix.

Enhanced flux pinning of silver-sheathed tapes with nano-MgO particle addition

Nano-MgO particles have been introduced into silver-sheathed (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x tapes fabricated by the rod-in-tube process. It is found that the transport properties of the nano-MgO particle doped sample are noticeably improved compared with those of the undoped sample. The irreversibility line of the MgO-doped sample shifts to higher temperatures and magnetic fields, as compared with the undoped sample. Therefore the introduction of nano-MgO particles can effectively enhance the flux pinning.