Huairuo Zhang

Controlled synthesis of CeO2 nanorods by a solvothermal method

Pure phase CeO2 nanorods (about 40?50?nm in diameter and 0.3?2??m in length) were synthesized through a solvothermal synthesis method. The addition of ethylenediamine is critical to obtain CeO2 nanorods. Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology. The reaction temperature and reaction time also had significant influence on the yield of CeO2 nanorods. A possible formation mechanism of CeO2 nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies. In addition, the optical properties of CeO2 nanorods were investigated. The UV?visible adsorption spectrum and photoluminescence spectrum of the CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively.

Wet chemical synthesis of gold nanoparticles using silver seeds: a shape control from nanorods to hollow spherical nanoparticles

A seed-mediated method was employed here for CTAB-assisted gold nanoparticle growth. 3–4 nm silver aqueous colloid was stabilized by sodium citrate and used as seed solution to initial gold particle growth. The concentration of seed solution was calculated based on its relationship with silver atom concentration and seed particle statistical mean volume. It was found that there is a maximum seed concentration of 8.57 × 10 −12 M( ∼25 μ l0 .343 × 10 −8 M seed solution added) in 10 ml 2.5 × 10 −4 M HAuCl4 growth solution for growth of rodlike particles. Below this seed amount, the aspect ratio of nanorods could be controlled by varying the silver seed amount, i.e. nanorods with aspect ratio ∼18.9 were obtained when the seed concentration in the growth solution was 0.343 × 10 −12 M by adding 1 μ l0 .343 × 10 −8 M silver seed solution and nanorods with aspect ratio ∼9.69 were obtained when the seed concentration in the growth solution was 1.715 × 10 −12 M by adding 5 μ l0 .343 × 10 −8 M silver seed solution. As the seed concentration in the growth solution was more than 8.58 × 10 −12 M( 25μ l0 .343 × 10 −8 M silver seed solution was added), there were no rodlike particles formed but spherical ones instead. These spheres were further studied by TEM and found to all be hollow structures. It was suggested that there were probably two different nucleation processes for growth of nanorods and spheres. For hollow spheres, the reaction between Ag seeds and Au ions formed hollow structures based on the Ag particle template effect. Then further growth of Au on these hollow structures produced hollow gold nanospheres. For nanorods, due to the very low concentration of silver seed (molar ratio of Ag seed: Au = 3.426 × 10 −8 ), the growth process here probably was started by silver-induced Au nucleation, in which reduction of gold ions by silver resulted in small gold clusters. These gold clusters further grew up into nanoparticles and nanorods in the presence of CTAB. S Supplementary data are available from stacks.iop.org/Nano/18/115608

Grain size dependence of mechanical properties in nanocrystalline selenium

Porosity-free nanocrystalline element selenium (nc-Se) samples with the mean grain sizes ranging from 8 to 70 nm were: synthesized by complete crystallization of the melt-quenched amorphous Se solid. Mechanical properties including microhardness (H-nu) and elastic modulus (E) of the nc-Se samples were measured by means of nanoindentation tests and microhardness tests, respectively. With a reduction of grain size, the nc-Se samples were found to be substantially hardened. But the grain size dependence of H-nu does not follow a simple Hall-Fetch relation over the whole grain size range, exhibiting three distinct stages corresponding to three different Hall-Fetch slopes. The maximum Hall-Fetch slope was found to be in the grain size range of 15-20 nm, corresponding to large values of the: elastic modulus. This behavior can be explained in terms of the lattice distortion in the nc-Se samples that was experimentally determined by using quantitative x-ray diffraction measurements. A conclusion is drawn that the lattice structure of the nm-sized crystallites may play an important role in mechanical properties of nanocrystalline materials.

K-doping induced peak effect in melt-textured grown YBa2−xKxCu3Oy crystals

K-doping YBa 2-x K x Cu 3 O y +40mol%Y 2 BaCuO 5 crystals with x = 0, 0.1 and 0.2 have been fabricated successfully by the melted-textured growth method. X-ray diffraction patterns reveal that the crystals are single phase except for the Y211 peak and the length of the c-axis does not change with the increase of K-doped concentration. The magnetization curves for the H//c-axis show a second peak in the temperature range 25-70 K. The temperature dependence of the characteristic field H p for the second peak of J c (H) and H max f for the peak of F p (H) shows a linear behaviour, but the temperature dependence of the characteristic field H d for the dip of J c (H) gives an exponential relation. The possible source of these behaviours is thought to be connected with the certain inhomogeneous distribution of K (different x) in the melted-textured grown YB(K)CO, which leads to a distribution of different T c clusters.

Peak effect in the MTG-YBa2−xNaxCu3Oy single crystals

Abstract We have measured the magnetic hysteresis loop of the melted-textured-growth YBa 2− x Na x Cu 3 O y ( x =0.1, 0.2) crystals in a wide range of temperature from 25 to 80 K (0.27⩽ T / T c ⩽0.89). The field dependence of the critical current density for a fixed temperature shows a peak effect. The field dependence of the pinning force density F p for all measured temperatures can be scaled into a single curve for the magnetic field H below the peak field H p . The dominant pinning mechanism in this low field regime is presumed to be normal-point-pinning. Above the peak field H p and near T c , an exponential H decay behavior of the critical current density was observed. The characteristic field H 0 can be deduced from the formula J c ( H )= J c (0)exp(− H / H 0 ) and can be presented as: H 0 ∝(1− T / T c w )/ α , in which α is 0.22 and 0.19 and T c w is 88.92 and 88.20 K, for x =0.1 and 0.2, respectively. A percolation-like network of inhomogeneous regimes induced by Na addition is discussed.