Yafeng Lu

The microstructures and superconducting properties of MgB2 bulks prepared by a high-energy milling method

We succeeded in the synthesis of high-Jc MgB2 bulks via high energy ball-milling of elemental Mg and B powder at ambient temperatures. Alternatively to longtime mechanical alloying technique, the mixed powder was ball-milled for only 1h and the completed reaction is achieved by subsequent annealing. The correlations among synthesis parameters, microstructures and superconducting properties in MgB2 bulks were investigated. Samples were characterized by XRD and SEM, and the magnetization properties were examined in a SQUID magnetometer. The highJc, approximately 1.7× 10 A/cm(15K, 0.59T), and improved flux pinning were attribute to a large number of grain boundaries provided by small grain size.

Kinetics of stabilized cubic zirconia formation from MnO2–ZrO2 diffusion couple

Microstructure and kinetics of the cubic phase formation are studied in ZrO2–MnO2 diffusion couple. During annealing in Ar, no other compounds are detected except the zirconia solution. With diffusion of Mn ions from manganese oxide to ZrO2, the cubic zirconia are found at the phase interface. The growth kinetics of the cubic zirconia solution layer in the submicrometer scale are analyzed. The growth behavior of the cubic zirconia layer is better described by the grain boundary diffusion model, and our experiment data exhibit a t1/4 dependence on time. The deviation from the experiment data to the theoretical value is also explained.

Growth and characterization of doped CeO2 buffers on Ni-W substrates for coated conductors using metal organic deposition method

CeO2 and Ce0.8M0.2O2−d films (M = Mn, Y, Gd, Sm, Nd and La) with (00l) preferred orientation have been prepared on biaxially textured Ni-W substrates by metal organic decomposition (MOD) method. The factors influencing the formation of cracks on the surface of these CeO2 and doped CeO2 films on Ni-W substrates were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM) analysis, atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The results indicate that many factors, such as the change of the ionic radii of doping cations, the transformation of crystal structure and the formation of oxygen vacancies in lattices at high annealing temperature, may be related to the formation of cracks on the surface of these films. However, the crack formation shows no dependence on the crystal lattice mismatch degree of the films with Ni-W substrates. Moreover, the suppression of surface cracks is related to the change of intrinsic elasticity of CeO2 film with doping of cations with a larger radius. SEM and AFM investigations of Ce0.8M0.2O2−d (M = Y, Gd, Sm, Nd and La) films reveal the dense, smooth and crack-free microstructure, and their lattice parameters match well with that of YBCO, illuminating that they are potentially suitable to be as buffer layer, especially as cap layer in multi-layer architecture of buffer layer for coated conductors.

Growth and structure of NdGaO3 films prepared by metal–organic deposition

Abstract We have successfully prepared NdGaO3 films with the (h00) preferred orientation on YSZ(100) single crystalline substrate by metal – organic deposition. The structure and morphology of the NdGaO3 films were investigated by X-ray diffraction and atomic force microscopy. It was found that the crystal orientation of the NdGaO3 films depends on the heat treatment temperature and time. An optimal growth condition for highly textured NdGaO3 films was obtained. The analysis by atomic force microscopy showed that the NdGaO3 films are smooth and pinhole-free. Our results showed that the NdGaO3 films prepared by the low-cost production method of metal – organic deposition could serve as a crystalline substrate with perovskite structure for many kinds of oxide electronic devices.

Fabrication of Cube-Textured Ni/Cu bi-Metallic Substrate

Abstract The influences of electro-depositing parameters on the formation of cube-textured Ni layer on Cu tape were studied. Results show that the cube texture can be obtained when the cathode potential is low enough and the pH value of electrolyte is in an appropriate range from 3 to 4. The influences of electro-depositing parameters could be explained by the geometrical selection theory. Finally, the thermal stability of texture of Ni layers was also investigated.