M. Peurla

Optimization of the BaZrO3 concentration in YBCO films prepared by pulsed laser deposition

YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with different concentrations of BaZrO3 ranging from c = 0.9 to 9.0 wt%. The critical temperature of the films decreases almost linearly with increasing BaZrO3 content whereas the critical current density shows a maximum near 3.9 wt%. In comparison with undoped YBCO films the accommodation field B* is considerably enhanced and the critical current density is improved in high fields in the films doped with BaZrO3, e.g. for c = 3.9 wt% by factor of 4.5 in a field of 5 T at 5 K. In the doped films the BaZrO3 particles grow epiaxially with YBCO. Transmission electron microscopy results show that the density of the BaZrO3 particles increases with increasing doping but the particle size remains practically the same (5–10 nm).

Structural Properties of YBCO Thin Films Deposited From Different Kinds of Targets

The accommodation field of YBa2Cu3O6+infin (YBCO) a thin films depends on the microstructure of the films and specifically the amount of pinning sites, which can be controlled by the type of the target used in the laser deposition. Typical values for the accommodation field at 5 K are 40-100 mT, 160 mT and 500 mT for films deposited from a micrograined, nanograined and optimally BaZrO3 (BZO) doped targets, respectively. We present structural data on YBCO thin films prepared by laser deposition from a nanograined target, a micrograined target and nanograined targets with added BZO. The characterizations were done with XRD and TEM and it was found that the main difference in the undoped films (nano and micro) was the stiffer lattice of the nanofilms. The BZO inclusions were found to induce a large amount of dislocations to the YBCO lattice surrounding the BZO. This can explain the increase observed in the accommodation field.

Magnetic relaxation and flux pinning in YBCO films prepared by PLD from a nanocrystalline target

The magnetic flux pinning properties of YBCO films prepared by pulsed laser deposition from nano- (n) and microcrystalline (μ) targets are studied and compared by magnetic relaxation and hysteresis measurements. The most striking difference between the films is the higher critical current density of the n-films (Jc(0 T,77 K) = 1 × 107 A cm−2) compared to the μ-films (Jc(0 T,77 K) = 3 × 106 A cm−2). The accommodation field B* that determines the end of the low field plateau of Jc is three times higher in the n-film than in the μ-film. In higher fields Jc(B) follows a power-law behaviour with exponents α = −0.6 in the intermediate field region and −2 in the high fields. The results are discussed on the basis of the recent strong pinning theories and it is concluded that the observed stronger pinning in the n-film is due to higher density of extended defects.

Crystalline orientation and twin formation in YBCO thin films laser ablated from a nanocrystalline target

Two sets of superconducting thin films were deposited on SrTiO3 by laser ablation, the first using a nanocrystalline target (n-films) and the second using a commercial microcrystalline target (μ-films). The effect of film thickness on the structure of the films was investigated using detailed x-ray diffraction analysis. It was found that for both types of film growth is a three-phase process, where at the beginning some grains with their a-axis perpendicular to the substrate surface are formed. In the second phase a purely c-axis oriented film is formed and in the last phase some a-axis oriented grains are again observed. The last phase was observed only for the μ-films. Both types of film were found to have equal numbers of c-axis oriented grains oriented with their a-axis to the = 0° and to the 90° direction. It was also found that the twin structure observed in both types of film develops much faster in the n-films, which might be the reason for the observed high critical current densities in n-films.

YBCO films prepared by PLD using nanocrystalline targets doped with BaZrO/sub 3/ or Y211

YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target and similar targets doped with BaZrO/sub 3/ or Y/sub 2/BaCuO/sub 5/ (Y211 phase) in order to investigate the effect of these impurities on magnetic flux pinning. The doped targets were pressed from nanopowders prepared by a sol-gel method from starting solutions whose nominal molar ratios corresponded to compositions YBCO+2.2 and 6.5 wt% BaZrO/sub 3/ and YBCO+3.0 wt% Y211 phase. The biggest changes in the superconducting properties relative to the films prepared from the pure target were observed in the films ablated from the BaZrO/sub 3/-doped targets. Although the doping reduces the critical temperature, the critical current density calculated from the hysteresis loops is significantly increased in external magnetic fields above 0.15 T. Addition of Y211 to the target is found not to be as effective for improving the flux pinning of the films in high magnetic fields as addition of the BaZrO/sub 3/. J/sub c/s in zero field and 77 K were 1.2 MA/cm/sup 2/ in the pure YBCO film, 1.1 MA/cm/sup 2/ in the 2.2 wt% BaZrO/sub 3/ doped film and 3.2 MA/cm/sup 2/ in the 3.0 wt% Y211 doped film.

Experimental study of the magnetosuperconductor Ru Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10 − δ : Effect of Mo doping on magnetic behavior and T c variation

Mo doped ruthenocuprates

Superconducting Properties of Films Deposited From Micro-, Nanocrystalline and Optimally BZO-Doped YBCO Targets

{\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Mo}}_{x}{\mathrm{Sr}}_{2}{\mathrm{Eu}}_{1.5}{\mathrm{Ce}}_{0.5}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}

Effects of nanocrystalline target and columnar defects on flux pinning in pure and Ba Zr O 3 -doped Y Ba 2 Cu 3 O 6 + x films in fields up to 30 T

are synthesized for

Magnetism, upper critical field and thermoelectric power of the magnetosuperconductor RuSr2Eu1.5Ce0.5Cu2O10−δ

x=0.0

Magnetic field dependence of the critical current and the flux pinning mechanism in YBa 2 Cu 3 O 6 + x films doped with BaZrO 3

, 0.2, 0.4, 0.6, 0.8, and 1.0, and their magnetic and superconducting properties are studied. It has been found that the magnetic transition temperature