ORIGINAL PAPER E. Gourba Æ P. Briois Æ A. Ringuede´ Æ M. Cassir A. Billard Electrical properties of gadolinia-doped ceria thin films deposited by sputtering in view of SOFC application Received: 11 April 2003 / Accepted: 29 September 2003 / Published online: 26 May 2004 Ó Springer-Verlag 2004 Abstract Gadolinia-doped ceria (GDC) remains, up to now, the most promising candidate for replacing yttria- stabilised zirconia (YSZ) as electrolyte for solid oxide fuel cells (SOFC) operating at intermediate temperature. Literature data point out that GDC could be used as electrolyte, anode material, or interlayers for avoiding the chemical interactions occurring at the interfaces. In the present work, GDC thin layers were produced by d.c. reactive magnetron sputtering and deposited over a thickness domain between 450 nm and 5.5 lm. According to our knowledge, the deposition of GDC sputtered layers has never been reported. The physico- chemical features of these thin films have been charac- terised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Impedance measurements have been carried out in order to determine the electrical properties of electrolyte thin films and in particular their ionic conductivity. Keywords Solid oxide fuel cell Æ Gadolinia-doped ceria Æ Thin layer Æ Sputtering Æ Impedance spectroscopy Introduction One of the solutions in order to reduce the SOFC operating temperature is the replacement of the state-of- the-art electrolyte, yttria-stabilised zirconia (YSZ). Nevertheless, this is not an easy problem because most of the materials with higher ionic conductivity than YSZ are also electronic conductors, which may induce potential losses and short-circuiting. Ceria-based oxides are probably the most interesting candidates for a new SOFC generation as electrolytes and/or as catalysts in the anode side, most particularly for methane oxidation [1, 2, 3]. Among the compounds of this family, gadolinia-doped ceria (GDC) seems to be the most suitable, but it can also be an electronic con- ductor due to the reduction of Ce 4+ at low oxygen par- tial pressures [4]. This redox reaction can be avoided either by adding a co-dopant to stabilise its structure [5, 6] or by reducing its thickness [7]. In the last case, an ultrathin layer of YSZ could act as an electronic barrier [8, 9]. In fact, combining the use of GDC with thin layer technology, including YSZ, can be a very efficient way to lower significantly the electrolyte resistance. Interesting results have been obtained with bi- or multi-layers of YSZ, YSB (yttria-stabilised Bi 2 O 3 ) and YDC (yttria- doped CeO 2 ) [10]. In the recent literature, different deposition tech- niques have been used to produce thin layers of the SOFC electrolyte, mainly YSZ but also YSB and YDC, by magnetron sputtering [10, 11, 12, 13], vacuum plasma spray [14], polymeric spin coating [15] and screen printing [16]. In a previous paper, we have shown the interest of using RF magnetron sputtering of oxide targets and atomic layer deposition (ALD) to produce homogeneous GDC layers of 1 to 5 lm on lanthanum- doped manganite (LSM) [17]. As far as we know, no other works have been dedicated to the elaboration of dense GDC thin layers with thickness less than 5 lm by sputtering. Moreover, very few systematic works on the electrical properties of GDC thin layers are available in the literature. Recently, electrochemical measurements have been carried out on nanocrystalline thin films of CeO 2 or Gd 3+ -doped CeO 2 deposited by screen printing on sapphire substrates: interesting correlations between microstructure and electrical conductivity have been described [15]. Presented at the OSSEP Workshop ‘‘Ionic and Mixed Conductors: Methods and Processes’’, Aveiro, Portugal, 10–12 April 2003 E. Gourba Æ A. Ringuede´ (&) Æ M. Cassir Laboratoire d’Electrochimie et de Chimie Analytique—UMR 7575, CNRS-ENSCP, 11 rue Pierre et Marie Curie, cedex 05, 75231 Paris, France E-mail: Armelle-Ringuede@enscp.jussieu.fr P. Briois Æ A. Billard Laboratoire de Science et Ge´nie des Surfaces—UMR 7570, Ecole des Mines, Parc de Saurupt, 54042 Nancy, France J Solid State Electrochem (2004) 8: 633–637 DOI 10.1007/s10008-004-0503-3