P. Mele

Enhanced high-field performance in PLD films fabricated by ablation of YSZ-added YBa2Cu3O7?x target

YBa2Cu3O7?x+Y2O3-stabilized ZrO2 (YBCO+YSZ) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin YSZ sector on top. The Jc at 77?K for the mixed YBCO+YSZ thin film was enhanced. The Jc at 77?K for the pure film and the mixed YBCO+YSZ thin film were 1.46 and 1.95?MA?cm?2 (self field) (and 0.09 and 0.28?MA?cm?2 (, B = 5?T)), respectively, even when both films were prepared using the same deposition conditions. The maximum pinning force of a doped film (77?K, ) was 15.9?GN?m?3, which is comparable to the value reached by NbTi at 4.2?K. In the YSZ-added sample, the angular dependence of Jc showed a broad peak at due to the flux pinning by the c-axis correlated defects. Elongated nanorods grown parallel to the c axis were consistently observed in the cross-sectional TEM images.

Insertion of nanoparticulate artificial pinning centres in YBa2Cu3O7- x films by laser ablation of a Y2O3-surface modified target

YBa2Cu3O7?x+Y2O3 (YBCO+Y2O3) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin Y2O3 sector on the top. The pinning properties for the mixed YBCO+Y2O3 thin film were strongly enhanced, especially at the temperatures lower than 77?K: the maximum global pinning forces FP for the Y2O3 doped sample are 7.8?GN?m?3 near 2?T at 77?K, 54.5?GN?m?3 near 4?T at 65?K, and 189?GN?m?3 near 9?T at 40?K. In the Y2O3-added samples, except for the plane configuration, the angular dependence of Jc showed a plateau, due to the flux pinning by isotropic pinning centres. Y2O3 nanoparticles randomly dispersed inside the YBCO matrix were consistently observed in the cross-sectional TEM images.

Effect of c-Axis-Correlated Disorders on the Vortex Diagram of the Pinning State

The introduction of the c-axis-correlated disorder is a promising technique for the improvement of the critical current density Jc for B\varparallelc of REBa2Cu3Oy (RE123) films and tapes. In order to understand the vortex pinning mechanism with the different variety of the c-axis-correlated disorder, the angular dependence of Jc was measured in detail for an Y123 film with BaZrO3 nano-rods, a Sm123 film with fine nano-particles and edge dislocations and an Y123 film with columnar defects introduced by the heavy-ion irradiation parallel to the c-axis. We found that the vortex pinning state for the variety of the c-axis-correlated pinning is similar in low fields below the matching field, but it shows different behaviors in high fields above the matching field. It is considered that the interstitial vortices interacted with the c-axis-correlated disorders through the vortex interaction may play an important role for the appearance of the c-axis-correlated pinning behavior in a high-field region above the matching field.

Vortex pinning phase diagram for various kinds of c-axis correlated disorders in RE123 films

The critical current density Jc and resistivity ρ of REBa2Cu3Ox (RE123) films were evaluated in high magnetic field and wide temperature regions. We use three different samples such as a heavy ion irradiated Y123 film, a BaZrO3 (BZO) added Y123 film and a low temperature growth Sm1-xBa2+xCu3Oy (LTG-Sm123) film. In these films, there exist the different c-axis correlated disorders like columnar shaped fission tracks for the heavy ion irradiated Y123 film, columnar shaped BZO precipitates for the BZO added Y123 film and edge dislocations at grain boundaries for the LTG-Sm123 films. The large peak of the angular dependence of Jc for B//c direction was observed for all samples measured in this study in a low field region, suggesting that the c-axis correlated pinning works well for these samples. However, we found that the behavior of the Jc peak for B//c strongly depends on a sort of c-axis correlated pinning centers. In the case of the columnar shaped fission tracks in the Y123 film, the Jc peak for B//c increases monotonically with increasing a magnetic field and seems to be connected with the dip structure in the angular dependence of ρ. In the case of the columnar shaped BZO precipitates, however, the Jc peak for B//c vanishes in a high field region above a few tesla and no dip behavior of ρ was observed. On the contrary, in the case of the edge dislocations for LTG-Sm123 film, the Jc peak for B//c shrinks with increasing field and almost vanishes. But it grows again with further increasing a magnetic field and the dip of the angular dependence of ρ is also observed. Hence the vortex pinning phase diagram strongly depends on a sort of c-axis correlated pinning centers. It is considered that these different behaviors of the Jc peak for B//c are related to the competition of the random and c-axis correlated pinnings.

J/sub c/ enhancement in YBa/sub 2/Cu/sub 3/O/sub x/ thin films by introduction of one-dimensional artificial pinning centers

A novel technology to introduce artificial pinning centers (APCs) into YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films prepared by pulsed laser deposition (PLD) was investigated for a drastic improvement of J/sub c/ in the films. Linear-like defects (one-dimensional APCs) were introduced perpendicular to the surface of the c-axis oriented films during the deposition process by using distributed Y/sub 2/O/sub 3/ nano-islands on substrates. The density of nano-islands was varied within 0.8-1.2/spl times/10/sup 10//cm/sup 2/ by PLD. A normalized resistivity as a function of temperature in magnetic fields shows a sharper resistivity drop for the film with APC, compared to pure YBCO film. J/sub c/ of the film with APC was also increased to 0.12 MA/cm/sup 2/ (77 K, B//c, 5 T), which was about two times higher than that of the pure YBCO film. The film had a very large J/sub c/ peak when the field was applied close to the c-axis. The peak J/sub c/ increased with the number density of Y/sub 2/O/sub 3/ nano-islands. This indicates that strong APCs parallel to the c-axis were incorporated into the YBCO film.

Fabrication of thick YBa2Cu3O7-x films on optimized SrTiO3 buffered-MgO single crystals

In this work, we studied the optimum deposition conditions for SrTiO₃ (STO) buffers deposited on MgO single crystals substrates by PLD method. We found that 120 nm thick STO films, deposited at 730 ^oC , present the smoothest surface and a minimum FWMH of the (002) reflection. High quality, smooth and free-crack (YBCO) thick superconducting films have then been fabricated using a deposition temperature of 800 ^oC on STO-buffered MgO substrates. A 373 nm thick YBCO/STO/Mg₂O film can carry current densities (77 K, 0 T) of 1.4 MA/ cm² and J_c (77 K, 5 T) of 1.4 MA/ cm² The J_c in high field overcomes the current transported in same experimental conditions by 180 nm thick YBCO film grown on Y₂O₃ -decorated STO single crystal. For 1350 nm thick YBCO/STO/MgO film the J_c (77 K, 0 T) is about 0.8 MA/cm² and J_c (77 K, 5 T) is 0.09 MA/cm².

Fabrication of Thick YBa 2 Cu 3 O 7− x Films on Optimized SrTiO 3 Buffered-MgO Single Crystals

In this work, we studied the optimum deposition conditions for SrTiO₃ (STO) buffers deposited on MgO single crystals substrates by PLD method. We found that 120 nm thick STO films, deposited at 730 ^oC , present the smoothest surface and a minimum FWMH of the (002) reflection. High quality, smooth and free-crack (YBCO) thick superconducting films have then been fabricated using a deposition temperature of 800 ^oC on STO-buffered MgO substrates. A 373 nm thick YBCO/STO/Mg₂O film can carry current densities (77 K, 0 T) of 1.4 MA/ cm² and J_c (77 K, 5 T) of 1.4 MA/ cm² The J_c in high field overcomes the current transported in same experimental conditions by 180 nm thick YBCO film grown on Y₂O₃ -decorated STO single crystal. For 1350 nm thick YBCO/STO/MgO film the J_c (77 K, 0 T) is about 0.8 MA/cm² and J_c (77 K, 5 T) is 0.09 MA/cm².

Inorganic nanocomposite films with polymer nanofillers made by the concurrent multi-beam multi-target pulsed laser deposition

We report on the new class of inorganic nanocomposite films with the inorganic phase hosting the polymer nanofillers made by the concurrent multi-beam multi-target pulsed laser deposition of the inorganic target material and matrix assisted pulsed laser evaporation of the polymer (MBMT-PLD/MAPLE). We used the exemplary nanocomposite thermoelectric films of aluminum-doped ZnO known as AZO with the nanofillers made of poly(methyl methacrylate) known as PMMA on various substrates such as SrTiO3, sapphire, fused silica, and polyimide. The AZO target was ablated with the second harmonic (532 nm) of the Nd:YAG Q-switched laser while PMMA was evaporated from its solution in chlorobenzene frozen in liquid nitrogen with the fundamental harmonic (1064 nm) of the same laser (50 Hz pulse repetition rate). The introduction of the polymer nanofillers increased the electrical conductivity of the nanocomposite films (possibly due to the carbonization of PMMA and the creation of additional channels of electric current) three times and reduced the thermal conductivity by 1.25 times as compared to the pure AZO films. Accordingly, the increase of the thermoelectric figure-of merit ZT would be ~ 4 times. The best performance was observed for the sapphire substrates where the films were the most uniform. The results point to a huge potential of the optimization of a broad variety of optical, opto-electronic, and solar-power nanocomposite inorganic films by the controllable introduction of the polymer nanofillers using the MBMT-PLD/MAPLE method.

Fabrication of Thick

In this work, we studied the optimum deposition conditions for SrTiO₃ (STO) buffers deposited on MgO single crystals substrates by PLD method. We found that 120 nm thick STO films, deposited at 730 ^oC , present the smoothest surface and a minimum FWMH of the (002) reflection. High quality, smooth and free-crack (YBCO) thick superconducting films have then been fabricated using a deposition temperature of 800 ^oC on STO-buffered MgO substrates. A 373 nm thick YBCO/STO/Mg₂O film can carry current densities (77 K, 0 T) of 1.4 MA/ cm² and J_c (77 K, 5 T) of 1.4 MA/ cm² The J_c in high field overcomes the current transported in same experimental conditions by 180 nm thick YBCO film grown on Y₂O₃ -decorated STO single crystal. For 1350 nm thick YBCO/STO/MgO film the J_c (77 K, 0 T) is about 0.8 MA/cm² and J_c (77 K, 5 T) is 0.09 MA/cm².