Growth of GdBa 2 Cu 3 O 7 thin films on single crystalline substrates of Y 1Àx Pr x Ba 2 Cu 3 O 7 R.F. Luccas a,1 , N. Haberkorn a,b,2 , J. Guimpel a,b,2 , G. Bridoux a,b,2 , G. Nieva a,b, * a Instituto Balseiro, U.N. de Cuyo and Comisio ´ n Nacional de Energı ´a Ato ´ mica, S. C. de Bariloche, 8400 R.N., Argentina b Comisio ´ n Nacional de Energı ´a Ato ´ mica, Centro Ato ´ mico Bariloche, S. C. de Bariloche, 8400 R.N., Argentina Available online 22 April 2007 Abstract Superconducting GdBa 2 Cu 3 O 7 thin films were grown by dc magnetron sputtering on Y 1Àx Pr x Ba 2 Cu 3 O 7 superconducting bulk single crystals. We optimized the in plane lattice matching with the Pr concentration. The samples were characterized by X-ray diffraction and electrical transport experiments. Magnetization hysteresis loops show high values of the critical currents for the films. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.62.Bf; 74.78.Bz; 74.78.Fk Keywords: Superconducting materials; High-T c films; Heterostructures Biaxial tensile or compressive stress has an important role in the physical properties of epitaxial thin films. To avoid in plane mis-orientation and crack formation it is necessary to minimize the lattice mismatch and the differ- ence in thermal expansion between substrate and film materials. For RBa 2 Cu 3 O 7Àd (R = rare earth or Y) super- conductors (R123), since the films are grown at high temperatures, defects and cracks are normally introduced during cool down at the tetragonal–orthorhombic struc- tural transition. The lattice parameters of the Y 1Àx Pr x Ba 2 - Cu 3 O 7Àd (YPr123) system diminish monotonically when decreasing x from the insulating Pr123 to the superconduc- ting Y123 [2]. Furthermore, the tetragonal–orthorhombic phase transition temperature decreases monotonically with increasing R ionic size. The oxygen is more disordered (higher entropy) in larger lattice parameter environments and the structural transition occurs at lower temperature [3,4]. In this work we present structural and superconducting properties of the mixed system (thin film-single crystal) composed by Gd123 films grown on YPr123 single crystals. The Pr concentration was chosen to optimize the epitaxial growth by matching the lattice parameters, resulting in a low disordered system with two different hole doping states, critical temperatures (T c ), and superconducting properties. The single crystals were grown with a flux method [5,6] using initial mixtures of Y 1Àx Pr x Ba 4 Cu 10 O y with x = 0.3 and 0.4. The as-grown crystals (typical dimensions: 1 · 0.5 · 0.03 mm 3 ) were annealed in flowing O 2 at 1 atmo- sphere for 10 days to increase oxygen homogeneity. X-ray characterization yields the expected structure and orienta- tion in our samples. Energy dispersive spectroscopy (EDS) in a scanning electron microscope indicates no impurities and a cationic ratio variation from x = 0.38 to 0.54. Each individual crystal (x = 0.4) in this study was checked for composition homogeneity. The Gd123 films (100–150 nm) were grown on selected crystals with smooth flux free sur- faces by dc magnetron sputtering, as described elsewhere [1]. 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.170 * Corresponding author. Address: Instituto Balseiro, U.N. de Cuyo and Comisio ´n Nacional de Energı ´a Ato ´mica, S. C. de Bariloche, 8400 R.N., Argentina. E-mail address: gnieva@cab.cnea.gov.ar (G. Nieva). 1 Current address: Institut de Cie ´ncia de Materials de Barcelona, 08193 Bellaterra, Barcelona, Spain. 2 Also at Consejo Nacional de Investigaciones Cientı ´ficas y Te ´cnicas. www.elsevier.com/locate/physc Physica C 460–462 (2007) 1377–1378