Liliang Ying

Thickness effect of La2Zr2O7 single buffers on metallic substrates using pulsed laser deposition for YBa2Cu3O7−δ-coated conductors

In the present work, the single buffer layers of La2Zr2O7 (LZO) with different thicknesses were prepared using pulsed laser deposition (PLD) on highly textured Ni?5?at.%W tapes for YBa2Cu3O7??-coated conductors. The highly textured LZO layers are obtained on the metallic substrates, making the subsequent epitaxial growth of superconducting YBa2Cu3O7?? layers feasible. The superconducting transition temperature increases as the LZO thickness increases up to 240?nm, achieving a value of Tc of more than 92?K with a narrow transition width less than 1?K. Inductive measurement reveals that the critical current density (Jc) reaches 0.77?MA?cm?2 at 77?K in self-field, showing that the single buffer of LZO is comparable to standard buffer architectures such as CeO2/YSZ/Y2O3 or CeO2/LZO. This implies that the LZO as a single buffer layer is promising for the simplification of the preparation process, leading to cost-effective coated conductors.

Heteroperovskite phase formation and magnetotransport properties of YBa2Cu3O7−x/SrRuO3 quasimultilayers

A series of quasimultilayers consisting of YBa2Cu3O7−δ (YBCO) and SrRuO3 (SRO), namely, p×(YBCO(m)/SRO(n)) (p: repetition periods; m: YBCO pulse number; n: SRO pulse number), is prepared on single crystal SrTiO3 by pulsed laser deposition. X-ray diffraction measurements reveal that a heterogeneous phase of Ba2YRuO6 is formed due to the chemical reaction, while both the in-plane and out-of-plane textures of the present quasimultilayers are as good as in the pure YBCO films. The content of Ba2YRuO6 increases as the pulse number of SRO increases, leading to the decrease in superconducting transition temperature (Tc). There is no obvious difference in Tc between the samples with the different deposition sequence orders of YBCO and SRO. The magnetic field dependence of critical current density (Jc) shows an enhanced flux pinning at relatively high fields for all the present quasimultilayers, which occurs at different ranges of fields depending on the applied temperatures. The Jc of the quasimultilayers can rea...

CRYSTALLIZATION AND MAGNETO-TRANSPORT CHARACTERISTICS IN MOD YBa2Cu3O7-δ FILMS

YBa2Cu3O7-δ (YBCO) films are prepared on the substrate of single crystal LaAlO3 (LAO) by using metal trifluoroacetates deposition (TFA-MOD). The phase evolvement, magneto-transport and flux pinning characteristics in MOD-YBCO films are studied. It is revealed that Ba-Cu-O and Y-Cu-O precipitates are formed and can be controlled by optimum crystallization process. The field dependence of Jc (H//c) shows that the accommodation field Hacc decreases exponentially with increasing temperature and the power-law relationship holds in the medium fields with an exponent α of about 0.67, nearly independent of temperatures. Compared with the samples grown by pulsed laser deposition, MOD films have larger Hacc at higher temperatures (> 50 K) indicating that the value of the exponent α is affected by the precipitates entrapped in the YBCO matrix.

Single and binary rare earth REBa2Cu3O7-delta films prepared by chemical solution deposition

In the present work, a series of single and binary rare earth REBa2Cu3O7-delta(REBCO, RE=Y, Ho etc.) thin films, such as YBCO, HoBCO and Y0.7Ho0.3BCO, were prepared by TFA-MOD process. Screw-growth mode and island-like surface were clearly observed in the present samples. Good c-axis orientation and high in-plane texture were identified in the all studied samples by measuring four circle X-ray diffractions (XRD). Theta-2Theta patterns of XRD showed no extra phases other than REBCO. As for HoBCO and Y0.7Ho0.3BCO thin films, the temperature dependences of resistance were investigated in various applied magnetic fields (< 9T) Irreversibility fields (Hirr), characterised with a criteria of zero resistance in R-T curves, showed a similar superconducting behavior between single and binary REBCO, i.e. no obvious changes in performance due to Ho doping in YBCO.

Epitaxial growth and thermal dynamics of CeO2 buffer layer on textured Ni-W substrates for YBCO coated conductors

In present study, the biaxially textured CeO2 buffer layers on Ni-W substrates have been prepared by chemical solution deposition (CSD) with cerium acetate as the starting precursor, mixed with solvents of Propionic acid, Isopropanol and Acetylacetone. Typical XRD θ-2θ scans and the pole figure display well out-of-plane and in-plane textures of CeO2 films. SEM and AFM results suggest that the buffer layer have uniform and smooth surface. Meanwhile, the effects of heating rate on CeO2 formation starting from the precursor solution have been studied using differential thermal analysis (DTA). And the further analysis is given by XRD results for precursor xrogel at the corresponding temperature. Detailed high temperature optical microscope (HTOM) photographs investigate the surface characteristics evolved with temperature.

Magneto-transport characteristics of superconducting RBa2Cu3O7-delta multilayers and quasi-multilayers

To study flux pinning modulation due to intentional adjustments of rare earth cations, layer sequences and island-like secondary phases, we built up a series of artificial multilayers consisting of binary rare earth R123 as well as quasi-multilayers consisting of Y123/M (M = oxides such as Yttria Stabilized Zirconia) on single crystalline SrTiO3 by pulsed laser deposition. The field dependence of transport critical current density Jc was measured at various temperatures and directions of the applied magnetic field. Comparing with pure Y123 films, almost all present multilayers and quasi-multilayers showed a crossover behaviour of flux pinning, evidenced by an existing medium field (Hcro) below which Jc is lower than of pure Y123 films, whereas above Jc is higher. Furthermore, a strong temperature dependence of such a crossover field was observed. The higher the temperature, the higer Hcro, implying that an artificial tailoring of flux pinning may appear in a narrow range of fields as the mixed vortex state moves towards to the region of weak vortex glass and vortex liquid. However, the improvement of flux pinning is hardly observed in the state of strong vortex glass.