A. Mitterdorfer 1 6 La 2 Zr 2 O 7 FORMATION BETWEEN YTTRIA-STABILIZED ZIRCONIA AND La 0.85 Sr 0.15 MnO 3 at 1373 K A. MITTERDORFER, L. J. GAUCKLER ETH Zurich, Department of Materials, Chair of Nonmetallic Materials, Swiss Federal Institute of Technology, CH–8092, Zurich, Switzerland gauckler@nonmet.mat.ethz.ch ABSTRACT Oxygen ion conducting Yttria-stabilized Zirconia and perovskite-type Sr-doped LaMnO 3 have been widely used as solid electrolyte and cathode materials in solid oxide fuel cells. The electrochemical properties of the cathode depend largely on the nanostructure and the phase composition of the interface between cathode and electrolyte. Interfaces between single crys- tals of 9.5 mol% Y 2 O 3 -stabilized ZrO 2 and sintered porous screen-printed La 0.85 Sr 0.15 Mn y O 3 (y = 0.95…1.10) were investigated. High resolution transmission elec- tron microscopy, electron diffraction and electrochemical impedance spectroscopy were employed for interface characterization. Atomic force microscopy and photoelectron spec- troscopy was used for surface studies of YSZ single crystals after dissolving the sintered LSM cathodes. Pyrochlore-type lanthanum zirconate formed at the interface during sintering at 1373 K. Nucleation, morphology, and growth kinetics was largely depending on cathode stoichiometry. Lanthanum zirconate formation was retarded and in case of A-site deficient perovskite. INTRODUCTION Increasing interest in operating solid oxide fuel cells (SOFC) at temperatures considera- bly lower than 1000 ˚C has raised the need for a better understanding of the factors limiting the performance of cathodes consisting of Sr-doped lanthanum manganites (LSM). The inter- action between cathode and electrolyte material which occurs during high temperature fabri- cation as well as under operating conditions is of particular interest. Pyrochlore-type La 2 Zr 2 O 7 and perovskite-type SrZrO 3 have been found to form at interfaces between yttria-stabilized zirconia (YSZ) and Sr- or Ca-doped LaMnO 3 at high temperatures in air [11]. The amount of La 2 Zr 2 O 7 formed has been found to decrease with increasing Sr or Ca substitution for La, and to increase with longer reaction periods or higher firing temperatures [2]. Yamamoto et al. [3] showed that lanthanum zirconate (LZO) formation during sintering is depressed with A-site deficient (La,Sr)MnO 3 . For non-stoichiometric material an incuba- tion period for zirconate formation was observed [4]. The purpose of the present work was to investigate the influence of manganese stoichi- ometry in LSM y upon nucleation and growth of LZO at the relativley low sintering tempera- ture of 1373 K in air. The study was performed with porous cathodes on YSZ single crystals. Atomic force microscopy (AFM) was used for topographic analysis of YSZ. Transmission Proc. of the Solid State Chemistry of Inorganic Materials, Pittsburgh, PA, Vol. 453 (1997), p. 425-430