Angular properties of pure and Ca-substituted YBa 2 Cu 3 O 7d superconducting thin films grown on SrTiO 3 and CeO 2 buffered Al 2 O 3 substrates A. Augieri a, * , G. Celentano a , L. Ciontea b , V. Galluzzi a , U. Gambardella c , J. Halbritter d , T. Petrisor b , A. Rufoloni a , A. Vannozzi a a ENEA Research Center, Via E. Fermi 45, 00044 Frascati, Rome, Italy b Technical university of Cluj-Napoca, Str. C. Daicoviciu 15, 3400 Cluj-Napoca, Romania c INFN-LNF, Via E. Fermi 40, 00044 Frascati, Rome, Italy d IHM, FZK, Postfach 3640, 76021 Karlsruhe, Germany Available online 14 April 2007 Abstract In this work transport properties of superconducting 10 at.% Ca-substituted YBCO thin films grown on (1 0 0)-SrTiO 3 single crystal substrate (STO) and superconducting pure and 10 at.% Ca-substituted YBCO thin films grown on CeO 2 buffered Al 2 O 3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction a the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between i defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a effect on grain boundary properties clearly emerged for 10 at.% Ca concentration. This effect is enhanced in sample grown 2 buf- fered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency. 2007 Elsevier B.V. All rights reserved. Keywords: Pinning; YBCO; Ca-substitution; Angular properties Most of the applicationsof superconducting YBa 2 - Cu 3 O 7d (YBCO) thin films are strictly related to the film currentcarrying capability. The improvement of critical current densities concerns both the study of grain bound- ary (GB) properties and the understanding of intragrain (IG) pinning mechanisms. Recently it has been proposed that partial substitution of calcium in yttrium site enhances YBCO GB critical current [1] although neither a clear trend in the GB transport properties nor a clear explanation of the Ca influenceon YBCO superconducting properties has emerged. On the other hand, evidences of strong c-axis correlated pinning have been observed in YBCO thin films grown on CeO 2 buffered sapphire substrates [2]. We report on transport properties analysis performed on 10 at.% Ca substituted YBCO (YCBCO) thin films grown on both (0 0 1)-SrTiO 3 (STO) and CeO 2 buffered r-cut sapphire sub- strates (CAO) and on pure YBCO films grown on CAO by PLD technique. Samples were patterned in order to obtai 50 lm wide and 1 mm long strips using standard UV pho- tolithography and wet etching methods, and then mount in a He gas flow cryostat provided with a 12 T supercon- ducting magnet with magnetic field and bias current alwa in the maximum Lorentz force configuration. DC transpor characterization was performed recording resistivity vers temperature curves, q(T), and I–V curves as a function of temperature, applied magnetic field and angle, a, between magnetic field direction and the normal to the film surfac From the analysisof the q(T) curvesthe GB network 0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.086 * Corresponding author. Tel.: +39 06 94005994; fax: +39 06 94005393. E-mail address: augieri@frascati.enea.it (A. Augieri). www.elsevier.com/locate/physc Physica C 460–462 (2007) 829–830