H. Kai

Vortex Bose glass in ErBa2Cu3Oy films with size-controlled nanorods

Anomalous changes in irreversibility lines (ILs) and critical current properties depending on growth conditions were demonstrated in ErBa2Cu3Oy films with Ba–(Nb,Er)–O nanorods. Despite the formation of nanorods in the matrix at all growth temperatures (Ts), Bose-glass-like vortex pinning was strengthened with decreasing Ts. In particular, the behavior of ILs can be understood in terms of the morphology of introduced nanorods, and Ts strongly affects the vortex states. Our present study suggests the importance of optimization of growth conditions in the production process of rare-earth-based coated conductors containing nanorods as vortex-pinning centers.

Transmission electron microscopy characterization of nanorods in BaNb2O6-doped ErBa2Cu3O7−δ films

BaNb2O6-doped microstructures as artificial pinning centers in ErBa2Cu3O7−δ films were studied by transmission electron microscopy. The presence of nanorods, which contain niobium, was confirmed from bright-field images and elemental map images. The crystal structure of the nanorod was determined to be cubic perovskite. The lattice constant of nanorods in the ErBa2Cu3O7−δ film was in good agreement with the lattice constant of Ba(Er0.5Nb0.5)O3. Furthermore, parallel Moire fringes were observed in the bright-field images. It has never been confirmed by any other researchers that BaNb2O6 doped into the ErBa2Cu3O7−δ film transforms to Ba(Er0.5Nb0.5)O3 nanorods with a perovskite structure.BaNb2O6-doped microstructures as artificial pinning centers in ErBa2Cu3O7−δ films were studied by transmission electron microscopy. The presence of nanorods, which contain niobium, was confirmed from bright-field images and elemental map images. The crystal structure of the nanorod was determined to be cubic perovskite. The lattice constant of nanorods in the ErBa2Cu3O7−δ film was in good agreement with the lattice constant of Ba(Er0.5Nb0.5)O3. Furthermore, parallel Moire fringes were observed in the bright-field images. It has never been confirmed by any other researchers that BaNb2O6 doped into the ErBa2Cu3O7−δ film transforms to Ba(Er0.5Nb0.5)O3 nanorods with a perovskite structure.

Flux pinning properties of correlated pinning at low temperatures in ErBCO films with inclined columnar defects

The effect of c-axis correlated pinning on the critical current density at low temperatures under high magnetic fields was investigated on the basis of the transport critical current density and irreversibility field properties of an ErBa2 Cu3 Oy film with inclined columnar defects. We found that the contribution of correlated pinning on Jc decreased drastically with decreasing temperature under high magnetic fields above the matching field, but still retained more than a 60% enhancement at 13 K. These effects of correlated pinning can be described using a cooperative model based on a combination of correlated and random pinning. At low temperatures, the presence of a matching field limited the flux pinning force for correlated pinning in comparison with that of random pinning, while the ratio of the maximum pinning force of the correlated pinning to the random one was proportional to the inverse of the irreversibility field. This suggests that the low efficiency of correlated pinning at low temperatures ...

Effects of BaMO3 (M = Zr, Sn) Nanorods on Critical Temperature of ErBa2Cu3Oy Films

In order to study the degradation of critical temperature Tc for a coated conductor using nanorods, the relationship between Tc and nanorod shape was investigated by transmission electron microscopy for ErBa2Cu3Oy (Er123) films with BaZrO3 (BZO) and BaSnO3 (BSO) nanorods. The dependence of Tc on the BZO or BSO content was different, however, the nanorods interface density dependence of Tc was the same for both. Thus, the interface density of the nanorods controls Tc of the nanorod-added films. The different degradation in Tc between the BZO and BSO nanorod-added films originated in differences in the nanorod diameter and density.

Intrinsic Surface Resistance of YBCO Thin Films Under DC Magnetic Field

We investigated the dc magnetic field and temperature dependences of the microwave intrinsic surface resistance (<i>R</i>_s^int) of YBa₂Cu₃O_y (YBCO) superconducting thin films with various thicknesses. We used YBCO films from 100, 200, and 300 nm thick YBCO films deposited on CeO₂/Al₂O₃ substrates. The <i>R</i>_s^int is means the surface resistance of YBCO film without the dielectric loss of the substrates. The <i>R</i>_s^int was obtained from measured surface resistance (<i>R</i>_s) by using a phenomenological equation. The <i>R</i>_s was measured using the dielectric resonator method at 21.8 GHz. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films during the <i>R</i>_s measurements. The <i>R</i>_s^int of the YBCO thin films increased when the dc magnetic field was applied. These relations could be explained with the two-fluid model for high-frequency and high-magnetic field limits. The <i>R</i>_s^int ratio (defined as <i>R</i>_s^int (5T)/<i>R</i>_s^int (0T)) slightly decreased with the film thickness. These results indicate that the <i>R</i>_s^int of HTS films depends on the film thickness in the dc magnetic field and the <i>R</i>_s^int in a dc magnetic field may be related to the pinning center in the HTS films.

Flux pinning properties in BaMO3 (M=Zr,Sn) nanorod-introduced ErBa2Cu3Ox films

Flux pinning properties on the ErBa2Ca3O7 films with the nanoscaled and columnar-shaped BaMO3 (BMO,M=Zr,Sn) precipitates, i.e., nanorods, were investigated systematically based on the microstructure, critical current density Jc and irreversibility field Bi properties in high magnetic fields. We found that the in-field Jc and Bi increase monotonically with increasing the nanorod density until 3.5 wt % BZO and 6 wt % BSO additions, respectively, although the critical temperature Tc is reduced. According to the flux pinning analysis assuming of the linear summation, the BSO doped samples have the higher performance of the flux pinning than the BZO doped samples quantitatively even after the reduction in the Tc and size of the nanorods. It is considered that those differences originate from the effective pinning length of the nanorods and/or the condensation energy due to the difference of the carrier density.

Cooperative Behavior of the Random and Correlated Pinning in Er123 Films With Columnar Defects

The flux pinning behaviors for the heavy ion irradiated Er123 films are investigated based on the detailed J_c(B,T,θ) properties. The double peaks of F_p curves for B//c appear in case of the matching field of 0.3 T along c-axis and 1.7 T tilted from c-axis. In addition, the peaks on J_c(θ) at θ = 0°(B//c), which originate from the columnar defects, decrease with increasing magnetic field but increase again near the irreversibility field. We found that the cooperation model of the c-axis correlated and random pinning centers can describe the observed double peak behavior of F_p(B) and the angular dependence of J_c related to the correlated pinning.

Influence of Growth Temperature on Microstructure and Superconducting Properties of

Influence of growth temperatures are discussed for microstructures and superconducting properties of films with nanorods grown by pulse laser deposition on substrates. The nanorods were observed in transmission electron microscopy images of the films. Nanorods were thinner and denser at a lower growth temperature. The performance in magnetic fields relates closely the morphology of introduced nanorods with growth temperature.Influence of growth temperatures are discussed for microstructures and superconducting properties of ErBa₂Cu₃O_7-delta films with Ba(Er_0.5Nb_0.5)O₃ nanorods grown by pulse laser deposition on SrTiO₃ substrates. The nanorods were observed in transmission electron microscopy images of the films. Nanorods were thinner and denser at a lower growth temperature. The <i>J</i> _C performance in magnetic fields relates closely the morphology of introduced nanorods with growth temperature.

{\rm ErBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}

We fabricated Fe(Se1−xTex) thin films on LSAT(100), MgO(001), R-Al2O3 substrates by ArF excimer pulsed laser deposition (ArF-PLD) and investigated pulse repetition rate dependence on film growth of Fe(Se1−xTex) thin films in ArF-PLD. Through x-ray diffraction measurements of Fe(Se1−xTex) thin films grown by ArF-PLD, 00l peaks of Fe(Se1−xTex) were confirmed in Fe(Se1−xTex) thin films grown by pulse repetition rate of 10 Hz but the 00l peaks were not confirmed in Fe(Se1−xTex) thin films grown at 5 Hz. Atomic force microscopy (AFM) revealed that 100 ~ 250 nm sized grains were formed on surface of the thin films grown at 10 Hz. It was found that the thin films grown at 5 Hz were formed thinner than those grown at 10 Hz, in spite of the same pulses. Energy dispersive x-ray spectroscopy (EDX) analysis revealed that composition elements of the thin films grown at 5 Hz were re-evaporated from them more than those grown at 10Hz. In ρ-T measurements of the thin films grown at 10 Hz, it was confirmed that the thin films has TConset = 6.5 ~ 10.5 K and TC0 of the Fe(Se1−xTex) thin film on an MgO substrate is 3.9 K.

Films With

Effects of vicinal growth in ErBa2Cu307−δ (ErBCO) with one-dimensional nanorods are discussed from their microstructures. BaNb2O6 doped ErBCO films were grown on vicinal substrates with tilted angles of 0°, 4° and 8° by a pulsed laser technique. Surface step structure appeared distinctly with increasing vicinal angles to 8° in images of scanning electron microscopy and atomic force microscopy. Then, Ba(Er0.5Nb0.5)O3 nanorods continuously grew from the step on vicinal substrate to film surface steps in transmission electron microscopy images of the film. The alignment of one-dimensional nanorods relate closely to film growth morphology.