We have performed cation diffusion experiments within the framework of the evaluation of long-term stability of gadolinium doped ceria acting as a reaction barrier between cathode and electrolyte materials. Diffusion couples were prepared depositing La(0.8)Sr(0.2)Co(0.2)Fe(0.8)O(x) (LSCF) thick films onto sintered Ce(0.9)Gd(0.1)O(1.95) (GDC) substrates by Pulse Laser Deposition (PLD). Interdiffusion across the LSCF/GDC interface was investigated by means of SIMS, at temperatures of 1000-1200 degrees C and times from 30 h up to 672 h. A significant diffusion of lanthanum into GDC and diffusion of cerium and gadolinium into LSCF were observed. In contrast, only shallow depth profiles for strontium, iron and cobalt into GDC were observed. X-ray diffraction (XRD) reveals the probable formation of lanthanum doped ceria (LDC) in the vicinity of the interface. Finally, the temperature dependence of lanthanum and strontium diffusion coefficients in bulk GDC is described by the following equations in the temperature range indicated: La in GDC : D(bulk)/m(2) s(-1) = 4.2 x 10(-5) exp (-390 kJ mol(-1)/RT) (1273 - 1473 K); Sr in GDC : D(bulk)/m(2) s(-1) = 1.1 x 10(-7) exp (-390 kJ mol(-1)/RT) (1373 - 1473 K). The grain boundary diffusion of lanthanum is, at least, five orders of magnitude faster than the bulk diffusion. (C) 2010 Elsevier B.V. All rights reserved.