L. Brunke

Flux pinning enhancement in YBa2Cu3O7−x films with BaSnO3 nanoparticles

Nanoparticles of BaSnO3 were incorporated into YBa2Cu3O7?x (YBCO) films on LaAlO3 substrates for magnetic flux pinning enhancements. More than an order of magnitude improvement in the high field magnetization Jc at 6?T at 77?K was observed as compared to regular YBCO films. The irreversibility field (Hirr) was increased to 8.5?T at 77?K and to 13.4?T at 65?K. The in-field transport current measurements confirmed an order of magnitude improvement in high fields. The angular dependence of the Jc data at 1?T showed that is 1.3 times higher than indicating the presence of c-axis correlated defects. Transmission electron microscopy studies revealed the presence of a large density of uniformly distributed ~10?nm sized BaSnO3 precipitates and strain fields around them. A dual sector pulsed laser deposition target is used to produce the films, thus eliminating reactions between BaSnO3 and YBCO during the target preparation stage, but may allow the BaSnO3 to react locally and create defects that act as pinning centres.

Enhancement and angular dependence of transport critical current density in pulsed laser deposited YBa2Cu3O7−x+BaSnO3 films in applied magnetic fields

YBa2Cu3O7−x (YBCO) films with nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical current density (Jct) of these YBCO+BSO films in applied magnetic fields and angular dependence of Jct on the applied field orientation was measured. It was observed that in the YBCO+BSO films, the Jct (H‖c orientation) increased considerably as compared to regular YBCO films and was 1.3 times higher than Jct in H‖ab orientation. Cross-sectional transmission electron microscopy images on YBCO+BSO films showed the presence of high density (3.5×1011cm−2) of nanoparticles (∼10nm size) and nanocolumns that extended throughout the thickness of the films with high density of dislocations and stacking faults (1000μm−2). The observed results of enhancements in Jct in H‖c and Jct in H‖ab orientations were discussed in the light of the observed microstructural details.

Biaxially textured constantan alloy (Cu 55 wt%, Ni 44 wt%, Mn 1 wt%) substrates for YBa2Cu3O7−x coated conductors

Commercially available constantan alloy rods (nominal composition Cu55?Ni44?Mn1?wt%) have been thermo-mechanically processed to develop biaxially textured substrates. It was found that the (001) recrystallization cube texture percentage could be increased from 72% to nearly 100% as the annealing temperature of the rolled substrates was increased from 750 to 1200??C. A full width half maximum (FWHM) of 6.5? in (111) phi scans and an FWHM of 4.9? in (100) omega scans were observed in the substrates annealed at 1200??C for 2?h. These substrates were found to have a Curie temperature of 35?K and so were paramagnetic at 77?K and ferromagnetic at 5?K with a saturation magnetization that is 2.5 times less than that of Ni?5?at.%?W substrates. Yield strengths of highly textured constantan substrates were found to be 1.5 times that of textured pure Ni substrates at room temperature.

Critical current density and microstructure variations in YBa2Cu3O7-x + BaSnO3 films with different concentrations of BaSnO3

Previous work on YBa 2 Cu 3 O 7− x (YBCO) + BaSnO 3 (BSO) films with a single composition showed significant critical current density ( J c ) improvements at higher fields but lowered J c in low fields. A detailed study on BSO concentrations provided here demonstrates that significant J c enhancement can occur even up to 20 mol% BSO inclusion, where typical particulate inclusions in these concentrations degrade the YBCO performance. YBCO + BSO films were processed on (100) LaAlO 3 substrates using premixed targets of YBa 2 Cu 3 O 7 -x (YBCO) with additions of 2, 4, 10, and 20 mol% BSO. The critical transition temperature T c of the films remained high (>87 K), even with large amounts (20 mol%) of BSO. YBCO + BSO films showed a gradual increase in J c at high fields as the amount of BSO was increased. More than an order of magnitude increase in J c was measured in YBCO + BSO samples as compared to regular YBCO at 4 T. YBCO + 10 mol% BSO films showed overall improvement at all the field ranges while YBCO + 20 mol% BSO was better only at high fields. Transmission electron microscopy revealed the presence of ∼7–8-nm-diameter BSO nanocolumns, the density of which increased with increasing BSO content correlating well with the observed improvements in J c .

Optimizing Flux Pinning of YBCO Superconductor With

Addition of nanophase defects to YBa₂Cu₃O₇ superconductor thin films enhances flux pinning, resulting in an increase in transport current densities (<i>J</i>_ct). While previous studies focused on single-phase additions, the addition of several phases simultaneously has shown strong improvements by combining different flux pinning mechanisms. This paper further explores the effect of mixed phase nanoparticle pinning, with the addition of insulating, nonreactive phases of BaSnO₃ and Y₂O₃. Processing parameters vary the BaSnO₃ concentration of 3, 5, and 10 vol. %, while maintaining Y₂O₃ constant at 3 vol.%. Pulsed laser deposition produces films on LaAlO₃ and SrTiO₃ substrates at deposition temperatures of 750-815°C. Current density is measured for fields ranging from <i>H</i> = 0 to 9 T with <i>H</i> // c, and temperatures from 5 to 77 K, providing a detailed picture of pinning effects. Optimized results of flux pinning, magnetic current densities <i>J</i>_cm (<i>H, T</i>), critical transition temperatures (<i>T</i>_c), lattice parameters, and microstructures are presented.

\hbox{BaSnO}_{3} + \hbox{Y}_{2}\hbox{O}_{3}

A special YBa₂Cu₃O_7-x (YBCO) target with a thin sector of second phase material, in this case either Y₂BaCuO₅ (Y211) or BaSnO₃ (BSO), was used to deposit YBCO films with non-layered nanoparticles on single crystal LaAlO₃ and biaxially textured Ni-5 at.% W substrates buffered with CeO₂ and YSZ layers(coated conductors). Although identical processing conditions were used, TEM images indicated that random Y211 nanoparticles in the case of YBCO + Y211, and evenly spaced BSO nanocolumns in the case of YBCO+BSO, form in the YBCO films. While YBCO plane buckling was observed at many places in the case of YBCO + Y211, a high density of stacking faults and dislocations were observed in the case of YBCO+BSO near the BSO columns. In transport critical current density (<i>Jc</i>) angular dependence measurements, the absence of nanocolumns in YBCO + Y211 films resulted in the absence of a peak at 0deg , <i>Jc</i>(<i>H</i>//<i>c</i>) , in <i>Jc</i> vs. thetas plots, as compared to a clear peak at 0deg observed in YBCO+BSO films with the nanocolumns. The in-field <i>Jc</i> measurements indicated small low-field <i>Jc</i> enhancements at 77 K in YBCO + Y211 films but more than an order of magnitude improvement in high-field <i>Jc</i> in YBCO + BSO films due to the differences in the microstructures.

Dual Mixed Phase Additions

In this paper, we have searched for superconductivity by measuring ohmic resistivity as a function of temperature in amorphous carbon films deposited by pulsed laser deposition and doped by ion implantation with sulfur and phosphorus ions. The doping concentrations were varied from 0.0003 to 4 Vol% for sulfur and 0.0003 to 1 Vol% for phosphorus. Previous efforts have studied doping of carbon-family materials such as highly oriented pyrolytic graphite, diamond-like carbon, and graphite/graphene, which have yielded critical temperatures lower than 20 K. In this study, amorphous carbon films doped with 2.55×1012 ions/cm2 phosphorus concentration showed a distinct change from semiconducting to metallic behavior and a dramatic 10 000-fold decrease in resistivity below 100 K as compared to undoped films. Sulfur-doped films with 2.55 × 1012 ions/cm2 concentration showed up to a 100-fold decrease in resistivity below 100 K as compared to undoped samples. While evidence of superconductivity was not observed, significant improvements in conductivity were noted below 100 K.

Comparative Study Between Similarly Processed

YBa2Cu3O7−x (YBCO)+BaSnO3 (BSO) thin films with BSO nanocolumns have been shown to have improved critical current density (Jc) in applied magnetic fields. Previously, a sectored target was used to grow thick (>2.5 μm) YBCO+BSO films. In the present study, a premixed YBCO+BSO (20 mol%) target was used to grow thick films (>3 μm) to determine if similar high quality thick films can be obtained as with the sectored target approach. In the case of the premixed target, BSO material is continuously supplied as opposed to the sectored target method. YBCO+BSO thick film samples processed using a premixed target were also found to have high Jc at high fields with Jc>104 A/cm2 at 8 T at 77 K, whereas typical YBCO films carry only 102 A/cm2. Transmission electron microscopy (TEM) on these films indicated that BSO nanocolumns with a diameter of ∼8–11 nm extend through the thickness of the films. The critical transition temperature (Tc) for the films was found to be ∼87 K, regardless of thickness.