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addition of yttria to the growing film [7 - 12]. The first technique provides excess yttriaonly in the very beginning of the growth, and the effect on the critical current density ismainly due to the formation of extended linear defects in the YBCO film overgrowingthe yttria nanoparticles. The second method has been implemented by direct addition ofyttria into the film by sputtering [8] or ablation [9], or by the use of targets with excessrare-earth element [10], and by sequential deposition of YBCO layers and intermediatequasi-layers of yttria [3, 11, 12]. In [7] the excess yttrium in the film resulted from thefeatures of the deposition technology. In these studies the yttria nanoparticles wereformed during the growth of the superconducting layer, and were overgrown by theYBCO matrix resulting in a 3D-net of pinning centers embedded in the superconductor.No suppression of superconductivity, or just a minor effect on T c [11] was observed insuch composites.In this paper we present results of our studies of yttria addition into YBCO filmsdeposited by PLD, by direct addition into the growing film by changing the targetelemental composition, and by yttria decoration of the substrate before deposition of thesuperconductor. The goal is to study the differences in the mechanisms of yttria additionon the film properties.2 Experimental methodsAll films were deposited by PLD, pulsed laser deposition (KrF excimer laser, λ = 248nm). The details of the deposition technique can be found elsewhere [13]. The depositionof superconducting layers was done in conditions optimized for the formation of highcrystal quality and high critical temperature thin YBCO films on perovskite substrates(770 ˚C, 0.8 mbar total pressure, Ar/O 2 = 8/2 sccm, laser energy density on target1.5 J/cm 2 , deposition rate 0.165 nm/s, post-deposition oxygenation in 500 mbar O 2 at450 ˚C for 1 hour). The films were mainly grown on (100) (LaAlO 3 ) .3 -(Sr 2 AlTaO 8 ) .7(LSAT) perovskite substrates, providing fine conditions for YBCO formation.A short optimization run was carried out to find the conditions for yttria particledeposition on the substrate surface, details will be published elsewhere. In brief, westudied the effect of pressure during ablation and of laser beam energy density on thetarget on size and density of nanoparticles formed on the substrate surface. The bestresults were obtained at substrate temperature 800 ˚C, Ar pressure 0.2 mbar, and energydensity of 1.1 J/cm 2 . At these conditions we observed nanoparticles of 40-70 nm indiameter and 20-45 nm in height, with densities up to 1500 μm -2 after 4000 pulses.An important feature of the prepared yttria layers is the presence of both uniform smoothfilm and nanoparticles embedded into this film. We used this effect to prepare twodifferent types of yttria layers: a uniform “seeding” layer, completely covering thesubstrate surface, and a “template” layer, consisting of individual nanoparticles withalmost no uniform film. The average thickness of both layers was 0.8 nm. All yttrialayers showed single (100) orientation. The lattice constant of the yttria layers was11.609 Å, close to that of bulk yttria (11.605 Å).The surface morphology of the films was studied by atomic force microscopy (AFM),and by scanning electron microscopy (SEM). The elemental composition of the filmswas found using EDAX analysis and inductively coupled plasma (ICP) analysis based onquantitative optical emission spectroscopy. The structural parameters were determinedby X-ray diffraction (XRD) measurements in Bragg geometry.3 Results and discussion3.1 Transfer of composition from target to YBCO filmIn PLD, the transport of material from target to substrate is a rather complicated processwith many parameters influencing the resulting composition (e.g. see [14]). We confinedRisø International Energy Conference 2011 Proceedings Page 239